Simtel MSDOS 1992 September/Simtel20_Sept92.cdr/msdos/cis/cis_b.arc/BPROTO.DOC

Text File | 1988-04-21 | 109KB | 2,784 lines

                    CompuServe Information Service

                        VIDTEX  4.0 Standards

                                 for

                      Terminal Emulator Programs










Copyright 1985
by CompuServe Incorporated, Columbus Ohio

                             April, 1985



















                                 NOTE

               The  information  in  this  document  is
               subject  to  change  without  notice and
               should not be construed as a  commitment
               by CompuServe Incorporated.













                              CHAPTER 1

                             INTRODUCTION



1.1  PURPOSE

The CompuServe information service is  a  low  cost  remote  computing
service  designed for use by the general public.  It is simple to use,
yet has many very powerful capabilities.  Similar in some respects  to
European   "viewdata"   systems,  the  service  is  based  on  a  tree
structured,  menu  driven  data  base.   The  data  base  consists  of
individual pages or "frames."

Currently  CompuServe  supports  a  terminal  standard  for   terminal
emulation   programs.    CompuServe  provides  a  series  of  terminal
executive programs  called  VIDTEX  which  implements  this  standard.
These  executives  implement a common set of features given the widely
varying  capabilities  of  microcomputer   systems.    This   document
describes  the features of the VIDTEX 4.0 software.  VIDTEX implements
error detection and retransmission protocols for the purpose  of  file
transfer and program loading.  This protocol is called the "CompuServe
B Protocol".

This document outlines the VIDTEX 4.0 implementation of the  following
capabilities:

     Video Processing
          Medium Graphics (128 x 96)
          Fine Graphics (256 x 192)
          Cursor positioning
     Terminal Loop Processing
     Meta Key Processing
     B Protocol
          Error detection.retransmission
          File transfer

In general, the Host computer will not  attempt  to  use  any  of  the
advanced   features   unless  the  <ESC>I  interrogation  response  is
implemented by the remote.  The interrogate response  tells  the  Host
which capabilities are implemented in the terminal.  If no response or
an unknown response is received from  the  <ESC>I  interrogation,  the
terminal  is  assumed  to  be  totally "dumb", with no cursor control,
graphics, color capability.
                                                              Page 1-2


An important exception to the interrogation  prerequisite  is  a  user
request for file transfer when the terminal type is known by the host.
The host software will present a menu of file transfer methods instead
of sending <ESC>I.
                                                              Page 1-3


1.2  CONVENTIONS USED IN THIS DOCUMENT

Throughout this document the following conventions are used:

<xxx> - denotes an ASCII control character where xxx is  the  standard
        name  of  the  character  (e.g.   <ESC>  is  the  ASCII Escape
        character, 1B hex).

<x>   - denotes a printable ASCII character (e.g.   <A>  is  an  ASCII
        upper case "A", 41 hex).

<nnn> - denotes the  ASCII  character  whose  value  is  nnn  decimal.
        Whenever an expression is given, it is always in decimal.

lower case denotes a variable  which  is  actually  substituted  by  a
        string of ASCII characters or a decimal value.

UPPER CASE denotes an ASCII character string exactly as shown.












                              CHAPTER 2

                     USER INTERFACE REQUIREMENTS



2.1  COMMUNICATIONS

If the computer has an internal modem, it must conform to  either  the
Bell 103  or  Bell 212  modulation  standards.   To  communicate  with
CompuServe, the modem must be set to originate mode and full duplex.



2.2  KEYBOARD

A full ASCII alphanumeric keyboard is required,  although  lower  case
and  most  control codes are optional.  Carriage return (control-M) is
necessary to log on.  If it can be detected that a key has  been  held
down  for  approximately  two  seconds,  it  should  auto-repeat.   If
hardware permits,  the  user  should  be  able  to  transmit  a  break
sequence.

VIDTEX 4.0 utilizes the concept of "meta keys"  to  permit  access  to
many  of  the  advanced  features.   The  keyboard implementation must
provide a means for the user  to  type  these  meta  keys.   Meta  key
encoding  has  precedence  over  control  key  encoding.   Control key
encoding has precedence over shift key encoding.   For  example,  Meta
and Control and "a" is Meta-A.  Meta and "a" is also Meta-A.

Some keyboards lack labeled keys for typing such  characters  as  "{",
"|",  "}", and "~" (7B though 7E hexadecimal).  VIDTEX should redefine
keys to allow the entire ASCII character set to  be  transmitted.   An
effort  should  be  made to relate the label on the redefined keys and
the characters generated.   For  example,  shift-[  could  be  "{"  or
control-!  could be "|".

A line of input from the keyboard is obtained in the following manner.
The  user  is  allowed  to type any displayable character (See Minimum
Video Display Requirements).  As a character is entered it  should  be
echoed  to  the  screen.   The  line  of  input can be terminated by a
carriage return or an ESCAPE.  Except in the case of file  names,  the
carriage  return  will  be  included in the line of input.  The ESCAPE
terminates the line but is not included.  Other control codes and meta
keys  are  not permitted in the input line.  During entry, the control
codes backspace and control-U will provide a simple  editing  facility
                                                              Page 2-2


for the user.  Note that backspace is destructive and control-U clears
the entire entry line.   The  entry  of  control-C  is  treated  as  a
control-U.   If  the  user  enters a Meta-A the line input function is
terminated and the abort status is passed to the calling routine.



2.3  MINIMUM VIDEO DISPLAY REQUIREMENTS

A minimum of 32 characters per line and 16 lines is required.  If  the
terminal  line  width  is  64  characters  or  greater, a double width
character option is desirable and should be  implemented  (see  Escape
Sequences).

The display should support the full ASCII character set although lower
case is optional.  The displayable characters are defined as the ASCII
characters <SPACE> through <~>, inclusive (20 through 7E hexadecimal).
If lowercase is not supported, all lowercase characters must be mapped
into the equivalent upper case characters.  If  the  display  hardware
does  not  support  the  correct display of some ASCII characters, the
video driver should map these characters to those  of  similar  shape.
Examples  of  commonly unimplemented characters include "{", "|", "}",
"~", "_", "^", and "\".












                              CHAPTER 3

                      VIDEO DRIVER REQUIREMENTS



3.1  TERMINOLOGY

In order to specify the video functions some terminology needs  to  be
introduced.

The home position refers to the upper left most character position  on
the  screen.   A  screen  line  is  a  grouping  of adjacent character
positions  which  appear  on  the  same  physical  screen  line.   The
character  position  preceding the first character on a screen line is
the last character position of the previous line, except for the  home
position  which  has  no  preceding character position.  The character
position following the last character on a screen line  is  the  first
character  position  of  the  next line, except for the last character
position on the last line which has no following character position.

A video operation is an operation which changes the contents of one or
more  character  positions, changes the cursor position, or alters the
mode of video operations.  A video  operation  can  be  as  simple  as
displaying  the next character or as complex as positioning the cursor
or changing screen colors.

The cursor is a means of representing the active  character  position.
A  video  operation  may  reference  the current cursor position.  The
current cursor position may be different following a video operation.



3.2  VIDEO INITIALIZATION

At program execution the  display  screen  should  be  cleared  and  a
program  identification  message  displayed.  The message should be in
the following format:

     "name Vv.e"

The first item is the program name, "name".  The numbers "v"  and  "e"
are the version and edit number, respectively.

The default mode is normal text mode and  the  default  screen  colors
should be chosen for display readability.
                                                              Page 3-2


3.3  TEXT MODE PROCESSING

3.3.1  Cursor Display

The cursor must be displayed on the  screen  by  some  means  such  as
reverse  video,  an underscore, or a graphic block.  The cursor should
be displayed following most video operations.  The cursor  should  not
be  displayed if it was not defined after the last operation or during
the processing of  a  video  operation,  including  the  reception  of
arguments during escape processing.



3.3.2  Text Display

A text character will be displayed by placing  the  character  on  the
screen  at  the  current cursor position.  The cursor is placed at the
following character position.



3.3.3  Scrolling

If a character is placed in the last position of the  last  line,  the
cursor  will  be placed at the first column of an imaginary line below
the bottom line.  The screen will not scroll until an attempt is  made
to actually display a character there.



3.3.4  ASCII Control Codes

The terminal must respond to the following ASCII control codes:



     3.3.4.1  <BEL> - Bell

     If the terminal has sound capability, it should  produce  a  bell
     (beep) sound.



     3.3.4.2  <BS> - Backspace

     The cursor is moved back one character position and replaces  the
     character which was previously there with a space.  If the cursor
     is on the first position  of  a  line,  it  should  move  to  the
     rightmost position of the previous line.  If the cursor is in the
     top left corner of the screen, no action should be taken.
                                                              Page 3-3


     3.3.4.3  <HT> - Horizontal Tab

     The cursor is moved  enough  character  positions  to  place  the
     cursor at the next tab stop.  Tab stops occur in the first column
     and every eight columns after that  (i.e.   columns  1,9,17,...).
     When  at or past the last tab stop on a line, a tab will move the
     cursor to the first position of the following line.



     3.3.4.4  <LF> - Line Feed

     The cursor is moved down one line without changing  its  relative
     horizontal  position.   If the cursor is on the bottom line, move
     the cursor down a line and scroll the screen one line so that the
     cursor is on the bottom line again.



     3.3.4.5  <FF> - Form Feed

     Clear the screen to blanks and position the cursor in  the  upper
     left corner.



     3.3.4.6  <CR> - Carriage Return

     Move the cursor  to  column  one  of  the  current  line  without
     destroying  the character there.  Note that if a <CR> is received
     after a character has been placed in the last column on  a  line,
     the  cursor  will  have wrapped to the first position on the next
     line.  In that nothing has been displayed,  the  carriage  return
     requires  the  cursor to move up one line.  The cursor should not
     be displayed (turned on) following a carriage return.



     3.3.4.7  Unimplemented Control Codes

     The video driver should ignore all other control codes.



3.3.5  Word Cleaning

The function of word cleaning is to attempt to prevent breaking  words
due to line wrapping.  This is accomplished by moving entire words (or
cleaning) to the next line.

                                                              Page 3-4


If a character has been displayed on the last character position of  a
line  and  the  next  character  is  a  space,  word  cleaning  is not
necessary.  If the next character is  a  displayable  character,  then
scan  the  line  backwards  looking for a space.  Scan no more than 20
positions.  If a space is not found, then place the next character  in
the first position on the following line.  Having searched and found a
space, copy each character between the space and the end of  the  line
to  the  next  line  and  place  a  space  in the character's original
position.   Place  the  character  received  in  the  next   available
location.

This makes it easier to read text  which  is  wider  than  the  screen
width.   For  example,  without  word  cleaning the following might be
displayed:

     Now is the time for all very good progra
     mmers to come to the aid of their countr
     y.

With cleaning, this would be displayed as:

     Now is the time for all very good
     programmers to come to the aid of their
     country.



3.4  VIDEO ESCAPE SEQUENCES

The Host  computer  will  not  attempt  to  use  the  following  video
functions   unless  the  <ESC>I  interrogation  is  implemented.   The
following  escape  sequences  are  defined  to  be  emulated  by   all
VIDTEX 4.0 compatible software.

In each case the given character is preceeded by an  escape  character
(1B  hex).   The  terminal  is responsible for converting the standard
protocol data into machine dependent functions and codes.   Data  that
is  inapplicable  to  a particular terminal should be simply discarded
(e.g., chroma bits on a black and white  unit).   All  characters  not
specifically  mentioned  are  reserved  by CompuServe Incorporated for
future expansion.



3.4.1  Video ESCAPE Sequence Summary

The following table summarizes the  video  escape  sequences  and  the
functions  they  perform.  Note the difference between lower and upper
case;  this is very important!

                                                              Page 3-5


          Sequence              Effect on Terminal

          <ESC><A>              Move cursor up one line
          <ESC><B>              Move cursor down one line
          <ESC><C>              Move cursor right one space
          <ESC><D>              Move cursor left one space
          <ESC><G><mode>        Change graphics mode
          <ESC><H>              Move cursor to the top left corner
          <ESC><K>              Clear from cursor to end of line
          <ESC><J>              Clear from cursor to end of screen
          <ESC><j>              Clear page - same as an ASCII Form Feed
          <ESC><l>              Set normal character width
          <ESC><m>              Set wide character width
          <ESC><Y><lin><col>    Set cursor position



3.4.2  <ESC><A> - Cursor Up

The cursor  is  moved  up  one  line  without  changing  its  relative
horizontal  position.   If  the cursor is on the top line, it wraps to
the same horizontal position on the bottom line.  The cursor must  not
destroy the character which was previously there.



3.4.3  <ESC><B> - Cursor Down

The cursor is moved  down  one  line  without  changing  its  relative
horizontal position.  If the cursor is on the bottom line, it wraps to
the same horizontal position on the top line.   The  cursor  must  not
destroy the character which was previously there.



3.4.4  <ESC><C> - Cursor Right

The cursor is moved right one column.  If the cursor is  at  the  last
column,  it  wraps  to  the  first  position on the next line.  If the
cursor is at the bottom right corner, it wraps to the top left corner.
The cursor must not destroy the character which was previously there.



3.4.5  <ESC><D> - Cursor Left

The cursor is moved left one column.  If the cursor is  at  the  first
column,  it  wraps  to  the  last column on the previous line.  If the
cursor is at the top left corner, it wraps  to  bottom  right  corner.
The cursor must not destroy the character which was previously there.
                                                              Page 3-6


3.4.6  <ESC><H> - Home Cursor

The cursor is moved to row one,  column  one.   The  cursor  must  not
destroy the character which was previously there.



3.4.7  <ESC><Y><lin><col> - Position Cursor

The cursor is positioned at the screen location specified by the  next
two  characters.   The  first character is the line number plus 31 and
the second character is the column number plus 31.  The home  position
is  located  at  cursor  position  line one, column one.  If a line or
column code falls outside the range of valid values, the invalid  code
is replaced by the valid code of nearest magnitude.



3.4.8  <ESC><G> - Graphics Mode Control

Graphics control is done by a three  character  sequence.   The  third
character determines the specific function.



3.4.8.1  <ESC><G><N> - Normal Mode

The video mode is reset to "normal"  mode  (text  only).   The  screen
should  not  be  changed  until the display of the next character.  In
this mode the parity bit is unpredictable.  Upon entering normal mode,
the  previous  state  of  the  graphics screen is unknown.  No graphic
character or image can be presumed to propagate to normal  mode.   The
return  to  normal  mode  is  typically  followed by a clear screen to
remove any graphic residues.



3.4.8.2  <ESC><G><H> - High Resolution Graphics

The screen is cleared to  black  and  high  resolution  graphics  mode
(256 x 192  pixels) is entered.  In this mode data is sent as pairs of
run length encoded  characters.   The  first  character  of  the  pair
indicates  the  number  of  background pixels and the second character
indicates the number of foreground pixels.  Each character of  a  pair
is the actual count plus 32.  In this mode, the parity bit is ignored;
thus, the maximum count that can be transmitted is 128-32, 96.

For  example,  the  ASCII  sequence   <L><W>   indicates   fourty-four
background  pixels and fifty-five foreground pixels.  The line drawing
should also wrap from the  last  position  on  a  line  to  the  first
position  on the next line.  Thus, if the last pixel set on a line was
in position 250 and a sequence of 0 background and  10  foreground  is
received, then the last six pixels are set on the current line and the
first four pixels are set on the next line.  The keyboard should  also
be left active while in this mode.
                                                              Page 3-7


3.4.8.3  <ESC><G><M> - Medium Resolution Graphics

The screen is cleared to black and  medium  resolution  graphics  mode
(128 x 96  pixels)  is  entered.   This  mode  is  identical  to  high
resolution except for the pixel size.



3.4.9  <ESC><K> - Clear To End Of Line

The screen is cleared from the current cursor position to the  end  of
the current line.



3.4.10  <ESC><J> - Clear To End Of Page

The screen is cleared from the current cursor position to the  end  of
the page.



3.4.11  <ESC><j> - Clear Page

The display is cleared and the cursor is positioned in  the  top  left
corner.    This   may   also  be  accomplished  by  a  form  feed  (0C
hexadecimal).



3.4.12  <ESC><l> - Set Normal Character Width

The display is set to its narrow character  size.   Note  that  normal
width character mode has more columns than wide character width mode.



3.4.13  <ESC><m> - Set Wide Character Width

The display is set to wide characters provided that wide mode  has  at
least 32 columns.












                              CHAPTER 4

                      TERMINAL LEVEL PROCESSING



4.1  INTRODUCTION

Terminal level refers to the highest level of program operation.   The
terminal  level  allows  "time  sharing" between the various input and
output   functions.    Mainly   terminal   processing   involves   the
transmission  of  characters  typed  by the user and the processing of
characters received from the host.



4.2  TERMINAL ESCAPE PROCESSING

Terminal level escape processing provides a means for coordinating the
activities of the host and the terminal.



4.2.1  <ESC><I> - Interrogate Remote

The terminal responds with a string which identifies its capabilities.
The format of the string is:

     <#>code<,>option list<CR>

The <#> implies the device is a VIDEOTEX-compatible unit.

The code is a three character string which identifies the manufacturer
and  model  of the terminal.  This is optionally followed by a version
and modification number.  Codes must be arranged by negotiations  with
CompuServe  Incorporated  in  order to maintain compatibility with our
host software.

The option list is a string of codes which indicates the features  the
terminal  supports.   The  option codes are separated by commas.  Each
option code implies that the terminal  supports  one  or  more  escape
sequences.

The <CR> marks the end of the response.

For example, the response:
                                                              Page 4-2


     #FRB24,CC,CW,G4,HC<CR>

indicates that the machine is a Frobitron computer running version 2.4
of  the VIDTEX program which supports cursor control, wide characters,
semigraphics 4, and a printer.



4.2.2  Video Enable And Disable

When an <ESC><e> sequence is  received,  the  video  is  disabled  and
subsequent  characters  are not displayed.  The video is enabled again
when an <ESC><f> sequence is received.  <ESC><e> and <ESC><f>  may  be
used  in  conjunction  with  <DC2>  and  <DC4> to direct output to the
printer without displaying it.



4.2.3  Keyboard Lock And Unlock

When an <ESC><b> sequence is received,  the  terminal  will  lock  the
keyboard  and  not  transmit  any  more  characters  typed.   Meta key
processing will also stop  in  that  the  keyboard  is  locked.   This
condition  is  reset  when  an  <ESC><c>  sequence is received.  These
sequences can be used by a host program which  does  not  want  to  be
interrupted during critical processing.



4.2.4  <ESC><ESC> - Hardware Specific Escape

This is  available  for  hardware  specific  functions  not  otherwise
available.   Their definition and implementation is the responsibility
of the hardware manufacturer.  CompuServe reserves the  right  to  not
support  any  hardware  specific  escapes  in  its host software.  The
development and support of the host software is the responsibility  of
the hardware manufacturer.

The VIDTEX 4.0 software should incorporate the following escape-escape
sequences.



4.2.4.1  Capture Buffer Control

Some common definitions for data capture control are:

     <ESC><ESC><O> - Open Ram Buffer
          The copying of incoming text to the  capture  buffer  should
          begin.
     <ESC><ESC><C> - Close Ram Buffer
          The capture buffer copying should stop.
     <ESC><ESC><Z> - Zero Ram Buffer
          The capture buffer should be emptied of all data.
     <ESC><ESC><V> - Transmit Ram Buffer
                                                              Page 4-3


          The  current  contents  of  the  capture  buffer  should  be
          transmitted to the host.
     <ESC><ESC><Y><pmt> - Transmit Ram Buffer with Prompt
          The  current  contents  of  the  capture  buffer  should  be
          transmitted  to  the  host.   After  transmitting a carriage
          return, VIDTEX should wait until the single character prompt
          is received before transmitting the next line to the host.



4.2.4.2  <ESC><ESC><W><lin1><col1><lin2><col2> - Window Control

Providing that the terminal supports a text display window,  the  size
and location of the window on the physical screen are to be set.  Each
argument is a row or column position masked by  the  addition  of  32.
The  argument pair, <lin1><col1>, specifies the upper-left-hand corner
of  the  window.   The  argument  pair,  <lin2><col2>,  specifies  the
lower-right-hand corner of the window.  The values for line and column
codes follow the rules of cursor positioning and the size of the  text
window  must  be  4  rows  by  11 columns or larger else the window is
removed automatically.  Word cleaning is disabled for windows  smaller
than 20 columns.

The SS option code allows the host to  interrogate  to  determine  the
size of the terminal's screen.  The values are transmitted in a manner
similar to absolute cursor positioning sequences.  The number of lines
is added to 31 before transmission.  The number of columns is added to
31 before transmission.



4.3  FLOW CONTROL

VIDTEX must recognize the  standard  ASCII  flow  control  characters,
<X-OFF>  (control-S  or DC3) and <X-ON> (control-Q or DC1).  If VIDTEX
receives  an  <X-OFF>  from  the  host,  it  must  halt   transmission
immediately.   If  an  <X-ON>  is  not  received in approximately five
seconds, transmission can be resumed.

VIDTEX expects the host to observe the same rules.   Flow  control  is
used  by  VIDTEX for delaying the host during remote processing and by
the user for regulating the rate of text display from the host.  There
are  several  instances  where an <X-OFF> is sent to stop transmission
from the host temporarily (RAM  buffer  almost  full,  printer  buffer
full,  menu selected).  Each time VIDTEX begins a remote process which
requires the host to wait, it will transmit an <X-OFF>  to  the  host.
Some  remote  functions  can contain multiple processing levels.  Each
level may user flow control.  To account  for  this  nesting  of  flow
control    transmissions,    VIDTEX   will   count   the   number   of
internally-generated <X-OFF>'s.

When a level of processing completes, it will request the transmission
of  an  <X-ON>.  When an <X-ON> is received by the host it will resume
transmission immediately, regardless of  how  many  <X-OFF>'s  it  has
received.  When an <X-ON> request is made, VIDTEX will first decrement
                                                              Page 4-4


the count of <X-OFF>'s sent.  If the count is zero  then  the  highest
level  of flow control has been reached and an <X-ON> is sent.  If the
count is non-zero then no <X-ON> is sent.

The user's use of flow control will have priority  over  flow  control
use   by  VIDTEX.   When  the  user  transmits  an  <X-OFF>  OR  <SOH>
(control-A), VIDTEX will not transmit  any  <X-ON>'s  until  the  user
types  an <X-ON>.  When the user's <X-ON> is transmitted, the count of
<X-OFF>'s sent by VIDTEX will be reset.  If the host does not  respond
to flow control, characters may be dropped.



4.4  PRINTER

Since a display type terminal leaves no record the user can refer back
to,  hardcopy  support  is  a desirable feature.  This is particularly
applicable to terminal emulator programs for microcomputers since most
microcomputers  can  support  a hardcopy printer.  The terminal should
allow both the host computer and the  terminal  user  to  control  the
printer.  The user can access the printer using a meta key.

The VIDTEX printer driver will convert standard ASCII  into  the  form
used  by  the printer.  Many printers lack horizontal tabs (as defined
in  the  video  driver  specification).   If  necessary,  VIDTEX  will
substitute the proper number of spaces for an horizontal tab.  Printer
output of tabular data should be identical to video output of the same
data.    If  the  printer  performs  a  <carriage  return><line  feed>
operation when given a carriage return, VIDTEX will  ignore  all  line
feeds that immediately follow carriage returns.  This will prevent the
printer output from appearing "double spaced."

When a <DC2> is received from the  host,  the  terminal  should  start
copying  all  received  data to the printer.  When a <DC4> is received
from the host, the terminal should stop  the  copying.   The  terminal
should have a buffer for the printer where characters may be placed if
the printer is busy.  When the buffer becomes within ten characters of
being  filled,  then  the  terminal  should  send  a <DC3> to stop the
transmission of data.  The  terminal  should  continue  to  empty  the
printer  buffer  until  the  buffer  is within ten characters of being
empty at which time a <DC1> should be sent to the host to resume  data
tranmission.  This buffering and flow control allows the use of a slow
printer at a higher data transmission rate.












                              CHAPTER 5

                      SIMPLE META KEY FUNCTIONS



Meta keys allow the user perform many local functions that users often
find  to  be  valuable.   For  greatest  speed  and  efficiency,  most
operations are typically accessed by holding the meta key and pressing
the  key  corresponding  to the desired function.  Less-used functions
are accessed via menus.



5.1  COPYING DATA TO THE PRINTER

If you type a Meta-R  on  the  keyboard,  a  copy  of  all  subsequent
characters  received  will be sent to the printer.  A Meta-T stops the
copying.



5.2  SCREEN PRINT

A printed copy of the entire screen should be provided by means  of  a
meta  key.   The particular key choice is not standard although Meta-*
and Meta-:  are currently in use.  This function cannot  be  performed
remotely.   Unless  the printer supports graphics, print screen should
ignore graphic images.  If the printer is not ready when screen  print
is  requested,  the  cursor  will  reappear.   The screen print can be
aborted by typing a Meta-A.



5.3  THE HELP PAGE

Meta-H should display a list of redefined keys and  a  list  of  those
characters substituted for improperly displayed ASCII characters.  The
user must key carriage return for terminal mode.
                                                              Page 5-2


5.4  MENU PAGE

Meta-M lists all available remote operations.  While  looking  at  the
menu, the user need only press the letter for the operation they want.
The meta key is not required.  Pressing carriage return will return to
terminal mode.

The menu message will provide information concerning the state of  the
Ram Buffer typically shown as follows:

     Used:  00000   Free:  00000

The  number  following  "Used:"   in  the  menu  indicates  how   many
characters  are  currently  stored  in  the  RAM  buffer.   The number
following "Free:"  indicates the number of unused characters available
in the RAM buffer.

As an option, the menu message may contain a  means  of  flagging  the
current  status  of  certain features.  Possible items to flag include
the status of word cleaning on/off and RAM buffer open/closed.



5.5  LOCAL VIDEO CONTROL

VIDTEX provides two local video control functions with  optional  wide
mode and text window control.



5.5.1  Screen Clearing

A meta key will be chosen to allow  the  user  to  locally  clear  the
screen.  Meta-CLR is an obvious choice.



5.5.2  Word Cleaning Control

A Meta-B will disable the word cleaning function of VIDTEX.  This  may
cause  words  to  start on the right edge of the screen and end on the
next line.  This mode is useful when you are typing out tables and  do
not  want  extra  spaces  inserted.   A  Meta-E  will  enable the word
cleaning function.



5.5.3  Wide Character Mode Control

If hardware permits a wide character video display mode (32 columns by
16  lines  minimum),  two  meta keys should be designated to allow the
user to switch between wide and normal display modes.  Meta-W for wide
mode and Meta-N for normal mode are currently in use.
                                                              Page 5-3


5.5.4  Text Window Control

As an optional feature, the VIDTEX video driver can allow the user  to
define the size and location of the "text display window."

At execution, the size of the window is the entire screen.  Some  meta
key  should  be  designated  to  allow  the user to set a new size and
location.  Meta-W is currently in use.  A set of  instructions  should
be  displayed  at  the  top of the current screen.  The user should be
allowed to position the cursor anywhere  on  the  screen  to  indicate
where the upper left hand corner of the new text display window should
be set.  When the cursor is  positioned,  the  user  presses  carriage
return.   The  cursor  is  then positioned to set the lower right hand
corner of the text window, and carriage return is pressed.  The window
is  now created.  The window must be at least 4 lines by 11 columns in
size or the window will be set to the full screen.  If the  window  is
less  than 20 columns word cleaning is disabled.  After the window has
been created or  removed,  the  cursor  is  positioned  to  the  upper
left-hand corner of the window.

Pressing Meta-A at anytime during the window creation sequence  should
abort  window creation and break the window to the full screen.  While
the window is in effect, all new text will appear inside  the  window,
including the menu and help pages.

The video driver should function within  the  window.   All  functions
valid  in normal and semigraphics 4 mode should work in "window mode."
Medium and high resolution modes will  remove  the  text  window  upon
entry  into  these  modes.   The  text  window will be set to the full
screen upon exit from medium and high resolution modes.

The window creation  process  specifies  a  rectangular  area  of  the
physical  screen  to  be  treated  as the current screen for all video
processing.  Each logical screen line  begins  at  the  same  physical
column  position.   Similarly each screen line ends at the same column
position.  All character positions outside the "active window"  should
never  be acted upon by the video driver.  Notably, when the cursor is
moved to the undefined character  position  past  the  last  character
position on the last line, the cursor should not appear.



5.6  VIDTEX 4.0 DISK VERSUS TAPE

VIDTEX is typically a disk-based program.  VIDTEX can  alternately  be
written  as  a  tape-based  program.  A tape version of VIDTEX will be
severely limited in terms of advanced capabilities.

The following descriptions will presume a disk-based system.
                                                              Page 5-4


5.7  INPUT TO DISK OPERATIONS

Whenever VIDTEX  requires  a  file  name  for  a  local  operation,  a
descriptive prompt will be displayed.  The user may enter a file name.
The file name will be a line of keyboard input (See Keyboard).

If the user enters a blank line at a  file  name  prompt,  VIDTEX  may
optionally  supply  an  appropriate  file  name.  This function is not
advisable for certain operations  such  as  "delete  a  file."   If  a
default  name  is  not supplied, VIDTEX should abort the function.  On
multi-drive systems, VIDTEX may optionally supply a default disk drive
identifier.   The  file  name string will be mapped into the character
set normally used by the computer's disk operation system.

VIDTEX should provide some means to notify the user in  the  event  of
any  disk errors.  If the operating system provides error message text
this text should be displayed to the user.  VIDTEX should also display
a  standard  error  text  identifying  that an error has occurred.  If
VIDTEX is not is autolog mode, the user should be  prompted  to  press
return  to continue.  The standard does not specify what action should
be taken if VIDTEX is in autolog mode.



5.8  FUNCTION KEYS

VIDTEX will provide function keys, each of which can be defined as any
arbitrary  text  string  the user chooses.  The minimum implementation
will include ten function keys, typically Meta-0 through  Meta-9.   In
application,  the  function  keys  are  useful  for  frequently  typed
commands.



5.8.1  Executing A Function Key

The execution of a function should provide the user with  convenience.
To  execute a defined function key, the user should need only to press
a dedicated function key or hold down  the  Meta  key  and  press  the
number  of  the function key.  This will start the transmission of the
key definition.  Typing Meta-A should abort a transmission once it has
started.



5.8.2  The Function Key Menu

The creation and storage of function key definitions are not  frequent
operations so these are handled from a menu accessed by typing Meta-F.
After typing Meta-F, the user should be presented with  a  menu.   For
example:

     Enter D to display the function key definitions
        or L to load definitions from disk
        or S to save definitions to disk
                                                              Page 5-5


        or the key to define (0-9):

The user may type Meta-A to return to terminal mode directly.



5.8.3  Defining A Function Key

The definition of a function key begins  with  Meta-F  to  access  the
menu.   The  user  should  be  prompted  to press the key they wish to
redefine.  The user need not  press  carriage  return.   VIDTEX  first
erases  the  the existing definition.  The user may then enter the new
definition.   The  creation  routine  should   accept   all   printing
characters  and  control  codes.   The routine need only display those
control codes supported by the video driver.  Unimplemented  codes  do
not  display.   If  a  carriage return is entered into a definition, a
line feed will also be displayed.  This is done to  make  the  display
readable.   To  end the definition, the user must type another Meta-F,
all other meta keys are discarded.  The user may clear a function  key
by  selecting  it  for  redefinition  and immediately typing a Meta-F.
This will cause the old definition to be erased without entering a new
definition.   The  total number of characters for all the function key
definitions will not exceed 255.



5.8.4  Displaying The Function Keys

To display the current definitions of all the function keys, the  user
should  type  a  Meta-F  and  select the display option (D).  Each key
number will be displayed followed by a colon and the  key  definition.
When  the  definitions  are  displayed,  a  line feed is automatically
displayed after a carriage  return.   This  makes  viewing  multi-line
function   keys  easier.   Note  that  only  the  carriage  return  is
transmitted when the function key is executed.

Once the function keys are displayed, the user can press the number of
the  key they want to execute (the Meta key should not be required) or
they can press "F" to return to the function key menu.



5.8.5  Function Key Disk Operations

The load and save function key options allow the user to keep  several
sets  of  definitions  with  different  filenames on disk at one time.
When VIDTEX is first executed, the function keys will be automatically
loaded from a specified file name.
                                                              Page 5-6


5.8.5.1  Saving The Function Keys

To save the function key definitions to disk, the user should  type  a
Meta-F  and select the save option (S).  VIDTEX will then prompt for a
file name.  If the file specified already exits on disk,  VIDTEX  will
delete  the  existing file without notifying the user that it existed.
The definitions will then be written to the file specified.  A  Meta-A
at  the  file  name  prompt should abort the save option and return to
terminal mode.



5.8.5.2  Loading The Function Keys

To load the function key definitions from a previously saved file, the
user should type a Meta-F and select the load option (L).  VIDTEX will
then prompt for a file name.  The existing definitions will be cleared
and replaced by those from the file.  Typing a Meta-A at the file name
prompt should abort the load option.  VIDTEX automatically  loads  the
definitions from a specified file name when it is first executed.



5.9  ABORTING A META FUNCTION

Most meta key operations should be aborted using  Meta-A.   Meta-Abort
during  window  creation  will  set  the  window  to  the full screen.
Meta-Abort will terminate any function key or RAM buffer transmission.
To  abort  the  creation  of a new auto-logon file, type Meta-A at the
file name prompt.  Once the file name is  entered,  the  Autolog  file
creation cannot be aborted.



5.10  EXITING VIDTEX

Meta-X will exit VIDTEX.  To prevent an accidental  exit,  VIDTEX  may
optionally  display  a message and request the user to verify the exit
request.  To continue the terminal session, the user must  reload  and
execute VIDTEX.

As an optional feature, VIDTEX will automatically load and  execute  a
program  (written  in  the native language of the computer) if certain
conditions are met at time of exit.  A typical implementation requries
three  components, all located one after another in memory.  First two
key letters such as "EX" must be present.  Next in memory will be  the
length  of  the  file  name  to  search for.  The length will be range
checked for validity.  Finally the file name  itself  will  be  stored
ascending in memory.  All of this information has to be present at the
time of exiting from of VIDTEX if auto load and execute on exit is  to
work.












                              CHAPTER 6

                            THE RAM BUFFER



VIDTEX will allow the user to save a copy of all  characters  received
in  the unused portion of RAM (the RAM buffer).  This is also known as
data-capturing since the received  data  is  saved  instead  of  being
discarded  as  soon as it is received.  The RAM buffer allows the user
to capture text from the host and save it for future reference.



6.1  DATA CAPTURE

When VIDTEX is first run the RAM buffer is empty and closed.  To  open
the RAM buffer and start saving the data, the user types a Meta-O.  An
informative message should  be  displayed.   All  subsequent  received
characters  will be added to the RAM buffer.  The RAM buffer is closed
by typing a Meta-C.  Again the  user  should  be  informed.   the  RAM
buffer  may  be opened again to add more to it.  The RAM buffer can be
zeroed (emptied) by typing a Meta-Z.   The  message  displayed  should
show if the RAM buffer was empty or if it was emptied by the Meta-Z.

If the RAM buffer becomes almost full, a message will be displayed and
a  control-S transmitted which immediately suspends host output.  This
gives the user a chance to save the buffer,  zero  it,  and  continue.
The user must type the control-Q to resume transmission from the host.
If the host does not stop transmission or the user types an  control-Q
without zeroing the buffer, it will automatically be closed.



6.2  SAVING THE SCREEN

A copy of the screen can be added to the RAM buffer by typing a Meta-G
(for  get  screen).   This  function  is  similar  to the screen print
function.  Each line is copied into the RAM  buffer  up  to  the  last
non-blank  character on the line.  After the last character on a line,
a Carriage Return/Line Feed is added.  If a line  is  entirely  blank,
only a Line Feed is added.
                                                              Page 6-2


6.3  VIEWING THE RAM BUFFER

The contents of the RAM buffer can be displayed by  typing  a  Meta-D.
The  display  should  stop  immediately  if  a control-S is typed.  To
resume the display, the user types a control-Q.  The  display  can  be
stopped  at  the end of a line (after the next line feed character) by
typing a control-A.  To cancel the display, the user  types  control-O
or  control-C.   A  message indicating that display has been cancelled
and a prompt to press carriage return to continue will  be  displayed.
When  the display of RAM buffer contents is done, a message indicating
end of buffer will be displayed and the user will be prompted to press
carriage return to return to terminal mode.

The RAM buffer will be printed by typing a Meta-P.   The  printing  of
the RAM buffer will be aborted by typing a Meta-A.



6.4  TRANSMITTING THE RAM BUFFER

Typing a Meta-V will transmit the RAM buffer continuously.   The  user
will  be  informed  that the transmission has begun.  The transmission
will stop only after all of the RAM buffer has been transmitted.  Flow
control  (Control-S  and Control-Q) from the host is recognized during
the transmission.  The transmission can be aborted by typing a Meta-A.

Typing a Meta-Y will initiate  a  prompted  transmission  of  the  RAM
buffer.   First  VIDTEX  will  prompt  for a prompt character;  then a
message displaying the prompt character will be displayed, and the RAM
buffer  will  be  transmitted one line at a time.  After each line has
been transmitted (a carriage return has been transmitted), VIDTEX will
wait for the prompt character specified to be received.  Note that the
first line of the RAM buffer  is  transmitted  before  prompt  seeking
begins.  The transmission can be aborted by typing a Meta-A.

The keyboard remains active during a  RAM  buffer  transmission.   The
keys  typed  by  the user should be transmitted with highest priority,
that is, without regard to prompt seeking or  the  transmission  of  a
line from the RAM buffer.



6.5  SAVING THE RAM BUFFER TO DISK

There are two ways to  save  the  RAM  buffer  to  disk:   edited  and
unedited.   The  edited save converts the ASCII data in the RAM buffer
data to the character set normally used by the computer.   An  attempt
should be made to map as many components of the ASCII and semigraphics
4 character sets into the native character set as the native character
set/video  driver  will  allow.  The unedited save will save a copy of
exactly what was received.  If the RAM  buffer  is  empty,  a  message
should  be  displayed  informing the user that the buffer is empty and
the save function aborted.

Typing a Meta-U will save the RAM buffer  to  disk  unedited.   VIDTEX
                                                              Page 6-3


will  first  prompt  for  the filename to save the RAM buffer to.  The
user may abort the save by typing a Meta-A at the file name prompt.

Typing a Meta-S will save an edited version of the RAM buffer to disk.
VIDTEX  will  first prompt for the filename to save the RAM buffer to.
The user may abort the save by  typing  a  Meta-A  at  the  file  name
prompt.   The  edited  save should be used for saving data to disk for
processing by another program.



6.6  LOADING THE RAM BUFFER FROM DISK

Typing a Meta-L will load the RAM buffer  from  a  disk  file.   First
VIDTEX  will  prompt  for a file name to load from.  Meta-A will abort
the load function.  All data in the file will be added to the  current
contents  of  the RAM buffer.  If the file is too large to load or the
buffer  becomes  full  after  the  load,  an  error  message  will  be
displayed.   If  the  error  message  is displayed, the user should be
prompted to press RETURN to continue.  During a RAM buffer load,  text
is inserted into the buffer until the buffer is full.












                              CHAPTER 7

                               AUTOLOG



Autolog allows the user to keep logon information for  many  different
systems.   It  also has the capacity to act in place of the user for a
number of applications.



7.1  CREATING A NEW AUTOLOG FILE

A new Autolog file will created with the following steps as  described
from the user's point of view:

1. First type a Meta-I.  You will then be  prompted  for  the  Autolog
   file  name  to write.  If you only press carriage return, a default
   file name will be used.  If the file already exists, it will  first
   be  deleted.   To  abort the autolog creation, type a Meta-A at the
   file name prompt.

2. You will then be asked for a prompt to wait for from the host.   If
   you  do  not want to wait for a prompt, just press carriage return.
   Otherwise  enter  the  host's  prompt.   The  prompt  sequence   is
   translated  to  upper  case  when  it  is  entered.   All  received
   characters are translated to upper case  for  testing  against  the
   prompt.  The maximum length for a prompt from the host is typically
   20 characters.  A prompt length of four to five characters or  less
   is recommended.  You may press the carriage return or ESCAPE key to
   terminate the prompt.  However, the carriage return  or  ESCAPE  is
   not included as part of the prompt.

3. You will then be asked for a  response  to  transmit.   Enter  your
   response  terminated  with carriage return or the Escape character.
   The carriage return will be transmitted  with  the  response.   The
   Escape  will  transmit no terminator when the response is sent.  If
   you enter just an Escape for  a  response,  an  empty  response  is
   indicated.   The  maximum  length  for  a  response is typically 64
   characters.   A  response  longer  than  the  maximum   number   of
   characters  per line can be transmitted by entering the response in
   two or more parts,  each  less  than  the  maximum  characters  and
   entering a null prompt between each part of the response.

4. Repeat the prompt/response sequence as many times as is  neccessary
                                                              Page 7-2


   to  complete  your  logon  sequence.   When  you have completed the
   sequence, enter a null entry at  both  a  prompt  and  a  response.
   After  you  have  completed  the  sequence,  VIDTEX  will return to
   terminal mode.

The prompt and response entries will be accepted as lines of  keyboard
input  (See Keyboard).  Note that the file may be optionally encrypted
on disk to protect the user's logon information.



7.2  EXECUTING AN AUTOLOG

To execute an autolog file, the user will press Meta-J.   VIDTEX  will
then prompt for the Autolog file name to read.  Pressing only carriage
return will select a default file name.  Note that autolog  lacks  the
capability  to  verify that the file specified is a true autolog file.
To abort the initiation of an autolog execution, the user must type  a
Meta-A  at the file name prompt.  If the file exists VIDTEX will enter
autolog mode.  VIDTEX will automatically exit autolog  mode  when  all
prompts  are  found  and  all responses are sent.  The execution of an
autolog can be aborted by typing a Meta-A.

The keyboard remains active during an autolog execution.  This  allows
the  user  to type during an autolog execution.  The keys typed by the
user should be transmitted with highest  priority,  that  is,  without
regard   to   prompt  seeking  or  the  response  if  currently  being
transmitted.



7.3  ADDITIONAL AUTOLOG FEATURES

VIDTEX 4.0 Autolog can do more than simply log  onto  a  host  system.
The  prompt  seeking function allows VIDTEX to act in the place of the
keyboard to provide a response to a host program.  Prompts can be  any
text that the host displays.

The response from autolog can be any text, control  characters,  or  a
command  to  VIDTEX  to  perform most any of the local meta functions.
The user can enter a control character into the response by typing  an
UP  ARROW then type the letter of the control key.  A meta key command
is entered into the response by typing LEFT ARROW then type the letter
of the meta key.

The user may obtain a delay of one  half  second  by  entering  Meta-&
(Meta-ampersand)  into a response.  A delay of two seconds is obtained
by entering  Meta-%  (Meta-percent)  into  a  response.   If  hardware
permits  carrier detection, VIDTEX should implement Meta-+ (Meta-plus)
as a meta key autolog response to delay until the modem indicates that
carrier  is  present  (carrier  detection).   VIDTEX  will delay after
carrier is present for 2 seconds to assure  that  carrier  is  stable.
Similarly,  a  delay until the modem indicates that carrier is lost is
obtained by entering Meta-- (Meta-minus)  into  a  response.   Meta-&,
Meta-%,  Meta-+,  and  Meta--  can  only  be  entered  into an autolog
                                                              Page 7-3


response and are not available from the keyboard or the Menu.

A single UP ARROW character is entered into a response by entering two
consecutive  UP  ARROWs.   Similarly  a single LEFT ARROW character is
also entered by two consecutive LEFT ARROWs.



7.4  AUTOLOG FILE CHAINING

The execution of a new Autolog file can be  started  from  an  already
executing  autolog  file.  When the Meta-J is executed from an Autolog
file, the current file is  closed  and  the  file  specified  is  then
executed.     The   contents   of   the   Autolog   file   after   the
"Meta-Jfilename<RETURN>" is ignored.



7.5  AUTOLOG EXAMPLES

A sample autolog creation sequence to logon  to  CompuServe  is  shown
below.

     Creating New Auto Logon
     Enter file name: compuserve auto  Select the file
     Prompt: <ESCAPE>                  Don't wait for prompt,
                                       transmit immediately
     Response: ^C<ESCAPE>              (<Up arrow><C>)
                                       Transmit a control-C
                                       with no carriage return
     Prompt: ID:                       Wait for 'USER ID:'
     Response: 70000,1                 Then send '70000,1'
     Prompt: word:                     Wait for 'PASSWORD:'
     Response: SECRET                  Then send 'SECRET'
     Prompt: !                         Wait until DISPLA
                                       prompts for input
     Response: GO HOM-1                Transmit 'GO HOM-1'
     Prompt: <ESCAPE>                  Terminate the input
     Response: <ESCAPE>                sequence by entering
                                       no prompt and no
                                       response

                                                              Page 7-4


The following Autolog could be used to get to the CB simulator program
from  most  any other menu on CompuServe.  The function key file named
"cb keys" must define key number 1 to be 'GO HOM-XX' where "XX" is the
page number of CB and key number 2 as the handle you want to use while
in CB.  HOM-21 is used for illustration only.  In this example a  left
arrow is represented by "-".

     Creating New Auto Logon
     Enter file name: cb auto          Select the file
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: <-FLcb keys             Load Function Keys
                                       from "cb keys"
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: T                       Send T for TOP
     Prompt: !                         Wait until top menu
                                       is displayed
     Response: <-1<ESCAPE>             Transmit Function
                                       Key One
     Prompt: ?                         Wait unitl CB prompts
                                       for handle
     Response: <-2<ESCAPE>             Transmit Function
                                       Key Two
     Prompt: <ESCAPE>                  Terminate the input
     Response: <ESCAPE>                sequence by entering
                                       no prompt and no
                                       response

The following shows how the autolog might execute.  It is initiated by
typing a Meta-J and responding with the the name "cb auto".

     T

     CompuServe            Page CIS-1
     CompuServe Information Service
     1 Home Services
     2 Business & Financial
     3 Personal Computing
     4 Services for Professionals
     5 User Information
     6 Index
     Enter your selection number,
     or H for more information.
                                  !GO HOM-21
     CompuServe           Page HOM-21

     Request Recorded,
     One Moment, Please
     Thank You for Waiting
     CB Simulator Ver 3(45)
     What's your handle? (your handle)
     (Channel) users tuned in
     Which channel: 1
     (1,Susana) Hi, CB'er

                                                              Page 7-5


The following example shows how the Autolog feature could be  used  to
set  the  communications  parameters  to  even  parity,  flow  control
disabled.  See the section "Modifying Communications  Characteristics"
for  details  on the Meta-Q function.  In this example a left arrow is
represented by "<-".

     Creating New Auto Logon
     Enter file name: setcom auto      Select the file
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: <-Q<ESCAPE>             Select Meta-Q
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: E<ESCAPE>               Set even parity
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: N<ESCAPE>               Set no flow control
     Prompt: <ESCAPE>                  Terminate the input
     Response: <ESCAPE>                sequence by entering
                                       no prompt and no
                                       response

The following  example  also  performs  the  same  function  and  then
initiates the Autolog file "login auto".  In this example a left arrow
is represented by "<-".

     Creating New Auto Logon
     Enter file name: setcom auto      Select the file
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: <-QEN                   Set the communications
                                       parameters
     Prompt: <ESCAPE>                  Don't wait for prompt
     Response: <-Jlogin auto           Start the Autolog file
                                       "login auto"
     Prompt: <ESCAPE>                  Terminate the input
     Response: <ESCAPE>                sequence by entering
                                       no prompt and no
                                       response



7.6  AUTOLOG AUTO START UPON EXECUTION

VIDTEX  will  automatically  enter  autolog   execution   if   certain
conditions   are   met.    A  typical  implementation  requries  three
components, all located one after another in memory.   First  two  key
letters  such  as  "AL"  must  be present.  Next in memory will be the
length of the file name to begin the autolog with.  The length will be
range  checked  for  validity.   Finally  the file name itself will be
stored ascending in memory.  All of this information must  be  present
at the execution of VIDTEX before auto start will work.
                                                              Page 7-6


7.7  MODIFYING COMMUNICATION CHARACTERISTICS

Meta-Q allows the user to  enable/disable  flow  control,  change  the
Parity  mode,  select  the  Baud Rate (if possible), change the Duplex
mode, and other communication parameters such as  printer  baud  rate.
Pressing Meta-Q will display the communications menu.  The menu should
indicate the current state of each feature.  The user  may  then  make
new  selections  for  each  feature.   Each  time the user makes a new
selection, the display should be updated.   The  user  types  carriage
return to return to terminal mode.

The disable flow control feature  will  disable  the  recoginition  of
received  flow control characters, but VIDTEX will still transmit flow
control to the host.

The parity modes available are 1) disabled, 8 bit data,  2)  Even,  3)
Odd,  4)  One,  and  5) Zero.  This feature only effects the parity of
characters typed by the user, or  auto  transmitted  from  an  autolog
response, function key execution, or RAM buffer transmission.

In Half Duplex mode, The character is echoed locally  by  calling  the
video  driver to display the character at the time it is placed in the
transmit buffer.  As an option, all ESCAPE  characters  typed  to  the
host will be diplayed as "$" to aid readability.












                              CHAPTER 8

                       B PROTOCOL:  PRIMITIVES



8.1  PURPOSE

The CompuServe B Protocol is used to provides an error-free  means  of
exchanging  information  between  a  remote terminal or computer and a
CompuServe  host  computer   by   means   of   error   detection   and
retransmission.   The  CompuServe  B Protocol will only be used if the
remote device responds to an <ESC><I> sequence with PB in  its  option
list.   B Protocol  disk transfer will only be used if the interrogate
response of the remote device includes the DT option.



8.2  GENERAL TERMINOLOGY

8.2.1  Terminal Mode

Terminal mode refers to the videotex terminal processing described  in
the first part of this document.



8.2.2  Protocol Mode

Protocol  mode  refers  to  the  special  processing  associated  with
protocol transmissions and function processing.  Protocol mode implies
an eight bit data path, disabled keyboard  processing,  nondisplay  of
received  data,  and  disabled termimal mode processing.  Protocol and
terminal modes are mutually exclusive in function.



8.2.3  File Transfer Mode

File Transfer mode refers to a special mode within protocol mode which
is  characterized  by  an uninterrupted protocol mode session in which
the transfer of a file is accomplished.
                                                              Page 8-2


8.2.4  Host

The host refers to the "master" portion of the protocol, the  computer
running  the  "master"  protocol and its associated telecommunications
network.  Only the host can initiate a B Protocol session.



8.2.5  Remote

The remote refers to the "slave"  portion  of  the  protocol  and  the
microcomputer or smart terminal running the "slave" protocol.



8.3  FLOW CONTROL

Flow control in protocol mode will regulate the transmissions  of  the
remote  only.   When  an XOFF (<DC3>) is received, the transmission of
data must cease immediately.  The transmission resumes upon  reception
of  an  XON (<DC1>).  The remote should never transmit flow control to
the host.



8.4  PROTOCOL BUFFER LEVEL TERMINOLOGY

8.4.1  Protocol Block Transmission

A block transmission refers to the transmission of  a  block  and  the
positive  acknowledgement  that the block was received correctly.  The
protocol block has several parts.



8.4.2  Block Number

Each block transmitted has a block number  associated  with  it.   The
block  number  is  modulo 10, thus the block number after 9 is 0.  The
block number verification logic refers to the number  of  the  current
block  and  to  the  number of the last previously verified block.  At
program execution, the last block number is set  to  0.   The  current
block  is  therefore  1.   Each  time a block is verified the terminal
emulator should increment the current block number.  The host protocol
logic must syncronize its block number with the terminal emulator, not
vice versa.



8.4.3  Command Field

The command field contains an ASCII string which specifies a  function
to be performed.  (See B Protocol Functions.)
                                                              Page 8-3


8.4.4  Block Contents

The content of the protocol block is the data needed  to  perform  the
function  specified.  The data is transmitted "transparently" so as to
allow the receiver to distinguish between data and control codes.



8.4.5  Transparency

Since some control  characters  are  used  by  the  protocol,  control
characters within the data are masked.  Control characters in the data
are transmitted transparently  by  the  sequence  <DLE><character+64>.
Using  this  rule a control-A (<SOH>) would be sent as <DLE><A>.  This
allows all 8 bit data to be transmitted unambiguously.  Currently, the
only  characters  that  NEED  to be transmitted transparently are ETX,
DLE, and ENQ.  The host may mask any other control  characters  during
transmission,  however,  and  thus  the  microcomputer must be able to
accept the masking of any character.  These rules apply  to  the  data
only  during  transmission;   the  data  is  converted to the original
character immediately upon reception.



8.4.6  Checksum

The "checksum" is a value used to detect any errors.  At the beginning
of every attempt to send a protocol block, the checksum is initialized
to zero.  Then, for each character in  the  block  starting  with  the
block  number  and  ending  with the <ETX>, the following algorithm is
applied.  The old checksum is rotated left one bit with  bit  7  being
rotated into bit 0;  the new character is added;  if carry occurs, one
is added to the checksum.  The checksum is  computed  from  real  data
only  (that  is,  after  transparency  masking  has been removed.) The
checksum is sent as a transparent character.



8.5  HOST PROTOCOL INITIALIZATION

The information required for the host  to  begin  a  protocol  session
consists of verifying that the remote has B Protocol and synchronizing
the host internal block number with the remote.

The host can determine if the remote  has  B Protocol  by  sending  an
<ESC><I>  in  terminal  mode.   The  remote  interrogate response must
contain "PB" for B Protocol and in addition  "DT"  for  file  transfer
mode.  (See Terminal Escape Processing)

The host may at any time during terminal processing transmit an  <ENQ>
to  the remote to obtain a positive acknowledgement which contains the
block number of the last block correctly transmitted.
                                                              Page 8-4


8.6  BLOCK TRANSMISSION

The transmission  of  a  protocol  block  involves  four  parts:   the
preparation,  the  actual  sending  of  the  block,  and  the logic to
error-detect and retransmit a bad block, and the  logic  to  recognize
the receiver's positive acknowledgement.



8.6.1  Preparation For Transmission

The remote will only transmit  a  protocol  block  in  response  to  a
protocol  function  request from the host.  Generally, the remote will
perform  the   required   function   before   sending   the   positive
acknowledgement   of   the  host  protocol  block.   Because  of  this
arrangement, the actions taken to prepare for  buffer  reception  will
still be in effect for buffer transmissions to the host.

The remote will begin reception of a protocol buffer when it  receives
a  <DLE>.   When the reception of a protocol buffer is intiated by the
host, the remote should (1) remember the  current  UART  masking  mode
(seven  or eight bit) and enter eight bit mode;  (2) close the capture
buffer to prevent the received block from  being  copied  to  the  Ram
Buffer;  and (3) disable the keyboard.



8.6.2  Actual Block Transmission

The actual transmission of  a  single  protocol  buffer  involves  the
following:
                                                              Page 8-5


8.6.2.1  Components Of A Block

The format of the B Protocol block as it is transmitted is:

     <DLE><B><blknum+48><command><contents><ETX><checksum>

 <DLE>  in  this  context  indicates  the  beginning  of  a   Protocol
     transmission.

 <B> indicates the start of a B protocol block.

 <blknum> is the sender's current block number.  The  receiver  should
     store  the  received block number for later comparison to its own
     internal block number.

 <command> field is  an  ASCII  string  which  indicates  the  desired
     function.

 <contents> field is the transparent data required by "command".

 <ETX> marks the end of the block.

 <checksum> is a value used to detect any  errors.   The  checksum  is
     initialized  to  zero.   The  received  checksum  is  transmitted
     transparently and must match the receiver's internally calculated
     checksum.



8.6.2.2  User Assurance

During long protocol sessions the user may come to  believe  that  the
protocol has died.  To avoid this situation the remote should diplay a
"+" on the user's screen for 32  characters  received  or  transmitted
during a file transfer session.



8.6.2.3  Maximum Block Length

The maximum  block  length,  from  the  initial  <DLE>  to  the  final
checksum,  not  including  transparent  characters  is  512.   If  the
terminal does not detect an <ETX> within this length, it has been lost
due to line noise and the block is bad.



8.6.3  Error Detection And Retransmission

The protocol logic will handle the following error conditions:
                                                              Page 8-6


     8.6.3.1  Unidentified Protocol Block

     The protocol block reception begins  with  <DLE>.   If  the  next
     character  received  is  not <B> then the remote will display the
     character on the screen and exit protocol mode.



     8.6.3.2  <NAK> Negative Acknowledge

     The receiver will send a <NAK> if any of the following situations
     occur:

         1) If the block number is incorrect (that is;   the  received
            block  number  is  neither the receiver's current nor last
            block number)
         2) the receiver times out
         3) the checksum is incorrect
         4) an <ETX> is not received within the maximum block length
         5) an <ETX> is received in terminal mode

     If the remote is in file transfer mode, the  value  of  the  last
     correctly  acknowledged  block  number should be displayed on the
     screen when a <NAK> is transmitted to the host.

     The sender will attempt to retransmit a block  ten  times  before
     aborting   its   attempts  and  switching  back  to  non-protocol
     communication.  If the remote is  the  sender  and  an  <ENQ>  is
     received,  the  remote  will  assume  failure  and retransmit the
     block.



     8.6.3.3  Failure Acknowledge

     In the event that an error occurred during function processing by
     the  receiver, it responds with a protocol block with a "command"
     field of <F> (for failure) and the "contents" field containing  a
     single  letter error descriptor.  The error descriptor can be one
     of the following:

       <N>  the function is not implemented
       <C>  there is a capacity problem (for example,  there  are  not
            that many pages, or there is no RAM at that address)
       <E>  an error occurred during  processing  (for  example,  disk
            errors)
       <A>  the user typed a Meta-A to abort the protocol function

       Once the failure block has been acknowledged by the  host,  the
       remote will exit protocol mode and file transfer mode if active
       and return to terminal mode.
                                                              Page 8-7


       8.6.3.4  Time Outs

       It is necessary to  define  some  time  outs  which  allow  the
       protocol  to  continue  even  if  some  control  sequences  get
       garbled.  This allows the  protocol  to  properly  recover  and
       continue.

       After the checksum for a block has been transmitted, the sender
       initiates  a  10  second timer.  If some type of acknowledge is
       not received within that time, the sender transmits an  enquire
       to  determine the status of the receiver.  The sender will wait
       ten more seconds  before  transmitting  another  enquire.   The
       sender will issue ten enquires before aborting the protocol and
       returning to non-protocol mode.

       When a block is being received, the receiver  should  wait  for
       ten  seconds  for  a character.  If one is not received in that
       time, it should assume that the <ETX> was garbled and  transmit
       a negative acknowledge.



  8.6.4  Positive Acknowledgement

  Once a block has been transmitted and processed without  error,  the
  receiver should send a positive acknowledgement to the sender.

  A special case of error handling  occurs  when  the  received  block
  number  is  not the current block number but the block number of the
  last  block  that  was  correctly   processed   and   the   positive
  acknowledgement  was  sent.   If  the  positive  acknowledgement  is
  grabled, the sender will retransmit the block again.  In  this  case
  the  receiver  should  discard  this  duplicate  block (since it has
  already been processed once) and send a positive acknowledgement  to
  the sender.

  If the sender receives a positive acknowledgement on the last  block
  correctly acknowledged, it will ignore the acknowledgement and await
  the  positive  acknowledgement  for  the  current  block  from   the
  receiver.

  The normal case is  when  the  received  block  number  matches  the
  receiver's  current  internal  block  number.  If no other error has
  occurred, the receiver will proceed to process the block.  Depending
  on   the   function,   the   receiver   may  transmit  the  positive
  acknowledgement before or after the processing of  the  contents  of
  the block.  If an error occurs after the the protocol block has been
  determined  to  be  correct,  the  error  cannot  be  communications
  related.   The  remote  should  transmit  a  failure  block  with  a
  "contents" field that describes the error.

  Once the positive acknowledgement has been transmitted to verify the
  correct  reception  of a protocol block, the receiver will increment
  its internal current block number.  Upon reception of  the  positive
  acknowledgement,  the  sender  will  increment  its internal current
                                                              Page 8-8


  block number.

  If the sender receives  a  <DLE><B>  indicating  the  initiation  of
  reception  of  a  new  block,  the  last  block  sent  is implicitly
  acknowledged.

  During  the  time  the  remote   is   awaiting   reception   of   an
  acknowledgement  from the host, any unrecognized characters received
  will be displayed on the user's screen.



       8.6.4.1  <ENQ> Enquire

       When the remote receives an <ENQ>, it responds with a  positive
       acknowledge  of the last block correctly received.  If an <ENQ>
       is received before any block is received, the receiver responds
       with  a  logical  acknowledge of block 0.  If <ENQ> is received
       during the reception of a block, the remote  should  abort  the
       reception,  send  the  positive  acknowledge  of the last block
       correctly received, and return to terminal mode.  The host  can
       also send an <ENQ> without placing the remote in protocol mode.
       This allows the host to synchronize its internal  block  number
       with the remote's internal block number.

       Since the remote must respond to XOFF, the XOFF  received  flag
       should be reset in case data 93 hexadecimal was received.



       8.6.4.2  <DLE><blknum+48> Positive Acknowledge

       When a block has been correctly received,  i.e.   checksum  and
       block  number  correct,  the receiver acknowledges the block by
       sending a <DLE><blknum+48>, where "blknum" is the block number.
       If  the  checksum  is correct but the block number is logically
       one less than the expected block number, the receiver transmits
       a  positive  acknowledge  and  ignores the block because it has
       already been processed  but  the  acknowledge  must  have  been
       garbled.  Note that block 9 is logically one less than block 0.

       Since the remote must respond to XOFF, the XOFF  received  flag
       should be reset in case data 93 hexadecimal was received.

       During file transfer  mode,  the  transmission  of  a  positive
       acknowledgement  will  also display the current block number on
       the screen.
                                                              Page 8-9


       8.6.4.3  <DLE><;> Wait Acknowledge

       When a block has been correctly received but it may  take  some
       time  to  process  the block, the receiver requests the host to
       wait by sending a <DLE><;>.  This tells the sender to wait  for
       ten seconds and then send an enquire.  The receiver should then
       respond to the inquire  with  another  wait  acknowledge  or  a
       positive acknowledge.  During the sender wait period the remote
       can send any valid protocol response (after function processing
       is  complete).   The  remote  may  send multiple <DLE><;>'s one
       after another to obtain prolonged wait periods between <ENQ>'s.



  8.7  EXITING PROTOCOL MODE

  The remote will exit protocol mode as follows 1) enable the keyboard
  if  not  in  file transfer mode, 2) restore the status of RAM buffer
  capture,  and  3) restore  the  data  mode  (7  or  8  bit)  to  its
  pre-protocol status.












                              CHAPTER 9

                   B PROTOCOL:  FUNCTION PROCESSING



The functions which presently can be performed with the B Protocol are
described below.



9.1  <B><LSB><MSB> BINARY LOAD

Memory is loaded with the data from the "contents" field  starting  at
the  location  <msb><lsb>.   This provides a mechanism for patches and
off-line programs to be loaded into the terminal or computer.  Address
space is limited to 16 bits, data to 8 bits.



9.2  <G><LSB><MSB> EXECUTE MEMORY

Control of the processor is transferred to the location <msb><lsb> via
a  subroutine  call.  The terminal must not hang up the modem and must
continue to function when  control  is  returned  via  a  return  from
subroutine.   The  positive  acknowledge  is  sent  before  control is
transferred so the host must allow time for the subroutine to  execute
before  attempting futher B Protocol communications.  Address space is
restricted to 16 bits.












                              CHAPTER 10

                   B PROTOCOL:  FILE TRANSFER MODE



10.1  INTRODUCTION

The B protocol provides a  method  for  transferring  files  from  the
Remote computer to the Host and vice-versa.  Most any type of file can
be transferred directly from disk to  disk.   Files  residing  on  the
Remote  computer's  disk  can optionally be erased or renamed from the
Host.

The B protocol is normally a noncontinuous protocol since  the  Remote
returns  to  text  mode  between  each  packet.   However, during file
transfer the Remote is be captive and is not allowed to return to text
mode  until  the  transfer  is completed.  For example, when a file is
being  transferred  from  the  Remote  to  the  Host,  the  Remote  is
continuously  sending  data  and  receiving  responses.   In  order to
preserve protocol integrity, the Remote must remove  itself  from  all
control of the user.  The only possible exception is allowing the user
to abort a transfer from the keyboard.  The Remote should  provide  an
indication  to  the user that the transfer is proceeding by displaying
block numbers and plus signs.



10.2  FILE TRANSFER TYPES

There are three types of file  transfer:   ASCII,  binary,  and  image
(machine  dependent).  The ASCII transfer is used to transfer standard
ASCII text.  The binary transfer is  used  to  transfer  binary  data.
This  could  be  used to facilitate the transfer of pure data from one
microcomputer to another.  The image  transfer  is  used  to  transfer
machine specific files (e.g.  object code, executable files).



10.2.1  ASCII Transfers

The download of an ASCII text file from the Host will produce  a  text
file  on disk containing an edited version of the text file in the the
Remote's native character set.

An ASCII upload to the Host performs the conversion  from  the  native
                                                             Page 10-2


acharacter  set  to  ASCII.  Any graphic characters that do not map to
ASCII will be replaced by space  on  upload.   Non-graphic  characters
that do not map to ASCII will be ignored.



10.2.2  Binary File Transfer

A binary upload will transfer the contents of the Remote's  disk  file
to the Host.  The contents of disk file will be uploaded exactly as it
is on disk.  The Host will store the file  contents  in  an  arbitrary
form for later download.

On download, the Host will provide the Remote with the contents of the
file just at it was earlier uploaded.  If the Remote computer supports
file types, the default file type on download will be chosen to be the
type most descriptive of binary data.



10.2.3  Image File Transfers

Image  file  transfer  will  transfer  a  header  containing  whatever
information  is  necessary to accurately recreate the file on download
and the contents of the Remote file.

The header  will  contain  1)  a  two  byte  (16  bit)  header  length
(transmitted Least Signifigant Byte, Most Signifigant Byte) and 2) the
machine identification code (See Interrogate Codes) as the next  three
bytes.   Additional bytes in the header (if any) will contain whatever
information is necessary for exact reproduction of the file.

On upload, the Remote will create the header  and  transmit  it.   The
contents of the disk file will follow.

On download, the Remote will first receive  the  header.   The  remote
will  use the information contained in the header to properly download
the disk file.  Note that the header length is generalized to 16  bits
and  that  the  header  may  span  a  protocol buffer.  If the machine
identification  code  of  the  header  does  not  match  the   machine
identification  code  of  the  Remote, the Remote will inform the user
that the file may not be compatible with their computer and prompt the
user  to  type  "Y"  for  Yes,  continue download or "N" for No, abort
transfer.  If the user continues, the header will  be  discarded.   If
the  user  aborts,  the Remote will respond to the host with a Failure
Abort block.



10.3  INITIATING A TRANSFER

Only the Host  can  initiate  a  transfer.   When  the  file  transfer
initiation  block  is  received,  the  remote will enter file transfer
mode.  The transfer initiate block is as follows:
                                                             Page 10-3


     <T><direction><type><file name>

          and <direction> is <U> or <D>

          and <type> is <A> or <B> or <C> or <I>

The  <T>  indicates  a  file  transfer  mode  control  command.    The
<direction>  character is either <U> for upload from Remote to Host or
<D> for download from Host to Remote.  Note that the <T>  command  has
other  arguments.   The  <type> defines the type of the transfer to be
performed as follows:

     <A>    ASCII
     <B>    Binary
     <I>    Image

The <file name> is the name of the file that the Remote  will  use  to
download to or upload from.



10.3.1  <T><D>  Download

This initiates the transfer of a file from  the  Host  to  the  Remote
computer.   If  the file already exists on the Remote computer's disk,
it responds with an Failure Error block;  it  must  not  overwrite  an
existing  file.   If there is not enough space on the disk, the Remote
will respond with a Capacity Failure block.  If an error occurs during
download,  the  Remote  will  delete  any  portion of the file that as
already been witten out to disk.  This will prevent the user from ever
mistaking a file fragment for a complete download.



10.3.2  <T><U>  Upload

This initiates the transfer of a file from the Remote computer to  the
Host  computer.  If the file is not found, the Remote responds with an
Failure Error block.



10.4  <N>  TRANSFERRING DATA

After a transfer has been initiated, the actual data  is  transmitted.
Each  block  of  data  has a "command" field of N for Next packet.  No
relationship exists between a packet of data and a physical or logical
record on the Host or the Remote.  Several records may be contained in
a packet and a record may span several packets.  The end of  a  packet
does not signify the end of a record.

The remote remains in file transfer mode throughout data transfer.
                                                             Page 10-4


10.5  <T><C>  COMPLETING A TRANSFER

When the sender of the file (Host or Remote) detects the  end  of  the
file,  it  sends a block with a "command" of <T><C> for Transfer Close
(the file).  The receiver closes the file and sends an  acknowledgment
on  the  close  request.  The transfer is then complete and the Remote
exits file transfer mode and returns to terminal mode.



10.6  ABORTING A TRANSFER

If the Host determines that the transfer can not be completed for  any
reason  (e.g.   line too noisy) or the Remote determines that the user
wants to abort the transfer, a Failure Abort  block  may  be  sent  in
response  to  or  instead of a data block.  If the Remote is sending a
file, it closes the file and returns to terminal mode.  If the  Remote
is  receiving  a  file, it closes the file, deletes it, and returns to
terminal mode.



10.7  <T><E>  ERASE A REMOTE FILE

This optional function is used to erase a file on the  Remote's  disk.
The function block is as follows:

     <T><E><file name>.

The command of <T><E> refers to Transfer Erase a file.  The "contents"
field  is  the  name  of  the file to be erased.  If the file does not
exist, is protected, or can not be erased for any  other  reason,  the
Remote responds with an Failure Error block.

This could be used to upload a file from the Remote and  once  it  has
been sucessfully transmitted, erase it.



10.8  <T><R>  RENAME

This optional function changes the name of a file that exists  on  the
Remote computer's disk.  The function block is as follows:

     <T><R><present><NUL><new>

The command is <T><R> for Transfer Rename a remote file.  The contents
of  the block is 1) <present> - the present name of the file, 2) <NUL>
- an ASCII null as a delimiter, and 3) <new> - the new  name  for  the
file.












                              APPENDIX A

                    CURRENTLY DEFINED OPTION CODES



  CB - Capture Buffer.  <ESC><ESC> O,C,Z,V,Y

  CC - Cursor control.  A, B, C, D, H, J, K, Y, and j

  CW - Wide character mode.  l and m

  DT - B Protocol Disk Transfer (in addition to PB).

  GH - High resolution graphics.  GH and GN

  GM - Medium resolution graphics.  GM and GN

  HC - Hard copy.  e and f (and <DC2> and <DC4>)

  SS<lin><col> - Screen Size (<lin> lines by <col> columns).

  PB - CompuServe B protocol.

  WC - Window Control.  <ESC><ESC><W>

  XX - Null Option Code.












                              APPENDIX B

    THE AMERICAN STANDARD CODE FOR INFORMATION INTERCHANGE (ASCII)                 ________



                  ASCII        Octal     Hex      Decimal
                Character      Value     Value     Value

                   NUL          000       00        000
                   SOH          001       01        001
                   STX          002       02        002
                   ETX          003       03        003
                   EOT          004       04        004
                   ENQ          005       05        005
                   ACK          006       06        006
                   BEL          007       07        007
                   BS           010       08        008
                   HT           011       09        009
                   LF           012       0A        010
                   VT           013       0B        011
                   FF           014       0C        012
                   CR           015       0D        013
                   SO           016       0E        014
                   SI           017       0F        015
                   DLE          020       10        016
                   DC1 (X-ON)   021       11        017
                   DC2 (T-ON)   022       12        018
                   DC3 (X-OFF)  023       13        019
                   DC4 (T-OFF)  024       14        020
                   NAK          025       15        021
                   SYN          026       16        022
                   ETB          027       17        023
                   CAN          030       18        024
                   EM           031       19        025
                   SUB          032       1A        026
                   ESC          033       1B        027
                   FS           034       1C        028
                   GS           035       1D        029
                   RS           036       1E        030
                   US           037       1F        031



                  ASCII        Octal     Hex      Decimal
                Character      Value     Value     Value

                   SP           040       20        032
                    !           041       21        033
                    "           042       22        034
                    #           043       23        035
                    $           044       24        036
                    %           045       25        037
                    &           046       26        038
                    '           047       27        039
                    (           050       28        040
                    )           051       29        041
                    *           052       2A        042
                    +           053       2B        043
                    ,           054       2C        044
                    -           055       2D        045
                    .           056       2E        046
                    /           057       2F        047
                    0           060       30        048
                    1           061       31        049
                    2           062       32        050
                    3           063       33        051
                    4           064       34        052
                    5           065       35        053
                    6           066       36        054
                    7           067       37        055
                    8           070       38        056
                    9           071       39        057
                    :           072       3A        058
                    ;           073       3B        059
                    <           074       3C        060
                    =           075       3D        061
                    >           076       3E        062
                    ?           077       3F        063



                  ASCII        Octal     Hex      Decimal
                Character      Value     Value     Value

                    @           100       40        064
                    A           101       41        065
                    B           102       42        066
                    C           103       43        067
                    D           104       44        068
                    E           105       45        069
                    F           106       46        070
                    G           107       47        071
                    H           110       48        072
                    I           111       49        073
                    J           112       4A        074
                    K           113       4B        075
                    L           114       4C        076
                    M           115       4D        077
                    N           116       4E        078
                    O           117       4F        079
                    P           120       50        080
                    Q           121       51        081
                    R           122       52        082
                    S           123       53        083
                    T           124       54        084
                    U           125       55        085
                    V           126       56        086
                    W           127       57        087
                    X           130       58        088
                    Y           131       59        089
                    Z           132       5A        090
                    [           133       5B        091
                    \           134       5C        092
                    ]           135       5D        093
                    ^           136       5E        094
                    _           137       5F        095



                  ASCII        Octal     Hex      Decimal
                Character      Value     Value     Value

                    `           140       60        096
                    a           141       61        097
                    b           142       62        098
                    c           143       63        099
                    d           144       64        100
                    e           145       65        101
                    f           146       66        102
                    g           147       67        103
                    h           150       68        104
                    i           151       69        105
                    j           152       6A        106
                    k           153       6B        107
                    l           154       6C        108
                    m           155       6D        109
                    n           156       6E        110
                    o           157       6F        111
                    p           160       70        112
                    q           161       71        113
                    r           162       72        114
                    s           163       73        115
                    t           164       74        116
                    u           165       75        117
                    v           166       76        118
                    w           167       77        119
                    x           170       78        120
                    y           171       79        121
                    z           172       7A        122
                    {           173       7B        123
                    |           174       7C        124
                    }           175       7D        125
                    ~           176       7E        126
                   DEL          177       7F        127












                              APPENDIX C

                    CONTROL CHARACTER DEFINITIONS



     NUL        Null, all zeroes         DC1  Device control 1 (X-ON)
     SOH        Start of heading         DC2  Device control 2 (T-ON)
     STX        Start of text            DC3  Device control 3 (X-OFF)
     ETX        End of text              DC4  Device control 4 (T-OFF)
     EOT        End of transmission      NAK  Negative acknowledge
     ENQ        Enquiry                  SYN  Synchronous idle
     ACK        Acknowledge              ETB  End of transmission block
     BEL        Bell, Alarm              CAN  Cancel
     BS         Backspace                EM   End of medium
     HT         Horizontal tab           SUB  Substitute
     LF         Line feed                ESC  Escape
     VT         Vertical tab             FS   File separator
     FF         Form feed                GS   Group separator
     CR         Carriage return          RS   Record separator
     SO         Shift out                US   Unit separator
     SI         Shift in                 SP   Space
     DLE        Data link escape         DEL  Delete












                                   APPENDIX D

                            ESCAPE SEQUENCE SUMMARY



Video Escape Sequences

     Sequence            Effect on Terminal

     <ESC><A>            Move cursor up one line
     <ESC><B>            Move cursor down one line
     <ESC><C>            Move cursor right one space
     <ESC><D>            Move cursor left one space
     <ESC><G><mode>      Change graphics mode
     <ESC><H>            Move cursor to the top left corner
     <ESC><K>            Clear from cursor to end of line
     <ESC><J>            Clear from cursor to end of screen
     <ESC><j>            Clear page - same as an ASCII form feed
     <ESC><l>            Set normal character width
     <ESC><m>            Set wide character width
     <ESC><Y><lin><col>  Set cursor position


Terminal Level Processing

     <ESC><I>            Interrogate Remote
     <ESC><e>            Disable Display
     <ESC><f>            Enable Display
     <ESC><b>            Disable Keyboard
     <ESC><c>            Enable Keyboard

     <ESC><ESC><O>       Open Ram Buffer
     <ESC><ESC><C>       Close Ram Buffer
     <ESC><ESC><Z>       Zero Ram Buffer
     <ESC><ESC><V>       Transmit Ram Buffer
     <ESC><ESC><Y><pmt>  Transmit RAM Buffer with prompt

     <ESC><ESC><W><lin1><col1><lin2><col2>     Window Control












                                   APPENDIX E

                               B PROTOCOL SUMMARY



Block Format:

     <DLE><B><blknum+48><command><contents><ETX><checksum>


Currently defined commands are:

 Remote Memory Reference

     B      Load memory
     G      Go execute at an address

 File Transfer Mode

     TE<file name>            Erase a file
     TR<present><0><new>      Rename a file
     TU<type><file name>      Transfer from Remote to Host
     TD<type><file name>      Transfer from Host to Remote
     N                        Next block of data
     TC                       Close file

          <type> is:
             A - ASCII
             B - Binary
             I - Image

 Failure Blocks

     FA Failure - Abort
     FC Failure - capacity problem
     FE Failure - error during processing of last block
     FN Failure - function not implemented



                     TABLE OF CONTENTS



Introduction  . . . . . . . . . . . . . . . . . . . . . . 1-1
  Purpose . . . . . . . . . . . . . . . . . . . . . . . . 1-1
  Conventions used in this document . . . . . . . . . . . 1-3
User Interface Requirements . . . . . . . . . . . . . . . 2-1
  Communications  . . . . . . . . . . . . . . . . . . . . 2-1
  Keyboard  . . . . . . . . . . . . . . . . . . . . . . . 2-1
  Minimum Video Display Requirements  . . . . . . . . . . 2-2
Video Driver Requirements . . . . . . . . . . . . . . . . 3-1
  Terminology . . . . . . . . . . . . . . . . . . . . . . 3-1
  Video Initialization  . . . . . . . . . . . . . . . . . 3-1
  Text Mode Processing  . . . . . . . . . . . . . . . . . 3-2
    Cursor Display  . . . . . . . . . . . . . . . . . . . 3-2
    Text Display  . . . . . . . . . . . . . . . . . . . . 3-2
    Scrolling . . . . . . . . . . . . . . . . . . . . . . 3-2
    ASCII Control Codes . . . . . . . . . . . . . . . . . 3-2
      <BEL> - Bell  . . . . . . . . . . . . . . . . . . . 3-2
      <BS> - Backspace  . . . . . . . . . . . . . . . . . 3-2
      <HT> - Horizontal Tab . . . . . . . . . . . . . . . 3-3
      <LF> - Line Feed  . . . . . . . . . . . . . . . . . 3-3
      <FF> - Form Feed  . . . . . . . . . . . . . . . . . 3-3
      <CR> - Carriage Return  . . . . . . . . . . . . . . 3-3
      Unimplemented Control Codes . . . . . . . . . . . . 3-3
    Word Cleaning . . . . . . . . . . . . . . . . . . . . 3-3
  Video Escape Sequences  . . . . . . . . . . . . . . . . 3-4
    Video ESCAPE Sequence Summary . . . . . . . . . . . . 3-4
    <ESC><A> - Cursor Up  . . . . . . . . . . . . . . . . 3-5
    <ESC><B> - Cursor Down  . . . . . . . . . . . . . . . 3-5
    <ESC><C> - Cursor Right . . . . . . . . . . . . . . . 3-5
    <ESC><D> - Cursor Left  . . . . . . . . . . . . . . . 3-5
    <ESC><H> - Home Cursor  . . . . . . . . . . . . . . . 3-6
    <ESC><Y><lin><col> - Position Cursor  . . . . . . . . 3-6
    <ESC><G> - Graphics Mode Control  . . . . . . . . . . 3-6
      <ESC><G><N> - Normal Mode . . . . . . . . . . . . . 3-6
      <ESC><G><H> - High Resolution Graphics  . . . . . . 3-6
      <ESC><G><M> - Medium Resolution Graphics  . . . . . 3-7
    <ESC><K> - Clear to End of Line . . . . . . . . . . . 3-7
    <ESC><J> - Clear to End of Page . . . . . . . . . . . 3-7
    <ESC><j> - Clear Page . . . . . . . . . . . . . . . . 3-7
    <ESC><l> - Set Normal Character Width . . . . . . . . 3-7
    <ESC><m> - Set Wide Character Width . . . . . . . . . 3-7
Terminal Level Processing . . . . . . . . . . . . . . . . 4-1
  Introduction  . . . . . . . . . . . . . . . . . . . . . 4-1
  Terminal Escape Processing  . . . . . . . . . . . . . . 4-1
    <ESC><I> - Interrogate Remote . . . . . . . . . . . . 4-1
    Video Enable and Disable  . . . . . . . . . . . . . . 4-2
    Keyboard Lock and Unlock  . . . . . . . . . . . . . . 4-2
    <ESC><ESC> - Hardware Specific Escape . . . . . . . . 4-2
      Capture Buffer Control  . . . . . . . . . . . . . . 4-2
      <W><lin1><col1><lin2><col2> - Window Control  . . . 4-3
  Flow Control  . . . . . . . . . . . . . . . . . . . . . 4-3
  Printer . . . . . . . . . . . . . . . . . . . . . . . . 4-4



Simple Meta Key Functions . . . . . . . . . . . . . . . . 5-1
  Copying Data to the Printer . . . . . . . . . . . . . . 5-1
  Screen Print  . . . . . . . . . . . . . . . . . . . . . 5-1
  The Help Page . . . . . . . . . . . . . . . . . . . . . 5-1
  Menu Page . . . . . . . . . . . . . . . . . . . . . . . 5-2
  Local Video Control . . . . . . . . . . . . . . . . . . 5-2
    Screen Clearing . . . . . . . . . . . . . . . . . . . 5-2
    Word Cleaning Control . . . . . . . . . . . . . . . . 5-2
    Wide Character Mode Control . . . . . . . . . . . . . 5-2
    Text Window Control . . . . . . . . . . . . . . . . . 5-3
  VIDTEX 4.0 Disk versus Tape . . . . . . . . . . . . . . 5-3
  Input to Disk Operations  . . . . . . . . . . . . . . . 5-4
  Function Keys . . . . . . . . . . . . . . . . . . . . . 5-4
    Executing A Function Key  . . . . . . . . . . . . . . 5-4
    The Function Key Menu . . . . . . . . . . . . . . . . 5-4
    Defining A Function Key . . . . . . . . . . . . . . . 5-5
    Displaying The Function Keys  . . . . . . . . . . . . 5-5
    Function Key Disk Operations  . . . . . . . . . . . . 5-5
      Saving The Function Keys  . . . . . . . . . . . . . 5-6
      Loading The Function Keys . . . . . . . . . . . . . 5-6
  Aborting a Meta Function  . . . . . . . . . . . . . . . 5-6
  Exiting VIDTEX  . . . . . . . . . . . . . . . . . . . . 5-6
The RAM Buffer  . . . . . . . . . . . . . . . . . . . . . 6-1
  Data Capture  . . . . . . . . . . . . . . . . . . . . . 6-1
  Saving the Screen . . . . . . . . . . . . . . . . . . . 6-1
  Viewing the RAM Buffer  . . . . . . . . . . . . . . . . 6-2
  Transmitting the RAM Buffer . . . . . . . . . . . . . . 6-2
  Saving the RAM Buffer to Disk . . . . . . . . . . . . . 6-2
  Loading the RAM Buffer from Disk  . . . . . . . . . . . 6-3
Autolog . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
  Creating a New Autolog File . . . . . . . . . . . . . . 7-1
  Executing An Autolog  . . . . . . . . . . . . . . . . . 7-2
  Additional Autolog Features . . . . . . . . . . . . . . 7-2
  Autolog File Chaining . . . . . . . . . . . . . . . . . 7-3
  Autolog Examples  . . . . . . . . . . . . . . . . . . . 7-3
  Autolog Auto Start Upon Execution . . . . . . . . . . . 7-5
  Modifying Communication Characteristics . . . . . . . . 7-6
B Protocol:  Primitives . . . . . . . . . . . . . . . . . 8-1
  Purpose . . . . . . . . . . . . . . . . . . . . . . . . 8-1
  General Terminology . . . . . . . . . . . . . . . . . . 8-1
    Terminal Mode . . . . . . . . . . . . . . . . . . . . 8-1
    Protocol Mode . . . . . . . . . . . . . . . . . . . . 8-1
    File Transfer Mode  . . . . . . . . . . . . . . . . . 8-1
    Host  . . . . . . . . . . . . . . . . . . . . . . . . 8-2
    Remote  . . . . . . . . . . . . . . . . . . . . . . . 8-2
  Flow Control  . . . . . . . . . . . . . . . . . . . . . 8-2
  Protocol Buffer Level Terminology . . . . . . . . . . . 8-2
    Protocol Block transmission . . . . . . . . . . . . . 8-2
    Block Number  . . . . . . . . . . . . . . . . . . . . 8-2
    Command Field . . . . . . . . . . . . . . . . . . . . 8-2
    Block Contents  . . . . . . . . . . . . . . . . . . . 8-3
    Transparency  . . . . . . . . . . . . . . . . . . . . 8-3
    Checksum  . . . . . . . . . . . . . . . . . . . . . . 8-3
  Host Protocol Initialization  . . . . . . . . . . . . . 8-3
  Block Transmission  . . . . . . . . . . . . . . . . . . 8-4



    Preparation for Transmission  . . . . . . . . . . . . 8-4
    Actual Block Transmission . . . . . . . . . . . . . . 8-4
      Components of a Block . . . . . . . . . . . . . . . 8-5
      User Assurance  . . . . . . . . . . . . . . . . . . 8-5
      Maximum Block Length  . . . . . . . . . . . . . . . 8-5
    Error Detection and Retransmission  . . . . . . . . . 8-5
      Unidentified Protocol Block . . . . . . . . . . . . 8-6
      <NAK> Negative Acknowledge  . . . . . . . . . . . . 8-6
      Failure Acknowledge . . . . . . . . . . . . . . . . 8-6
      Time Outs . . . . . . . . . . . . . . . . . . . . . 8-7
    Positive Acknowledgement  . . . . . . . . . . . . . . 8-7
      <ENQ> Enquire . . . . . . . . . . . . . . . . . . . 8-8
      <DLE><blknum+48> Positive Acknowledge . . . . . . . 8-8
      <DLE><;>  Wait Acknowledge  . . . . . . . . . . . . 8-9
  Exiting Protocol Mode . . . . . . . . . . . . . . . . . 8-9
B Protocol:  Function Processing  . . . . . . . . . . . . 9-1
  <B><lsb><msb> Binary Load . . . . . . . . . . . . . . . 9-1
  <G><lsb><msb> Execute Memory  . . . . . . . . . . . . . 9-1
B Protocol:  File Transfer Mode  . . . . . . . . . . . . 10-1
  Introduction . . . . . . . . . . . . . . . . . . . . . 10-1
  File Transfer Types  . . . . . . . . . . . . . . . . . 10-1
    ASCII Transfers  . . . . . . . . . . . . . . . . . . 10-1
    Binary File Transfer . . . . . . . . . . . . . . . . 10-2
    Image File Transfers . . . . . . . . . . . . . . . . 10-2
  Initiating a Transfer  . . . . . . . . . . . . . . . . 10-2
    <T><D>  Download . . . . . . . . . . . . . . . . . . 10-3
    <T><U>  Upload . . . . . . . . . . . . . . . . . . . 10-3
  <N>  Transferring data . . . . . . . . . . . . . . . . 10-3
  <T><C>  Completing a Transfer  . . . . . . . . . . . . 10-4
  Aborting a Transfer  . . . . . . . . . . . . . . . . . 10-4
  <T><E>  Erase a Remote File  . . . . . . . . . . . . . 10-4
  <T><R>  Rename . . . . . . . . . . . . . . . . . . . . 10-4
Currently Defined Option Codes  . . . . . . . . . . . . . A-1
The American Standard Code for Information Interchange  . B-1
Control Character Definitions . . . . . . . . . . . . . . C-1
Escape Sequence Summary . . . . . . . . . . . . . . . . . D-1
B Protocol Summary  . . . . . . . . . . . . . . . . . . . E-1