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/*
HEADER: CUG113;
TITLE: 6800 Cross-Assembler (BDS C Version);
FILENAME: A68.DOC;
VERSION: 2.6;
DATE: 07/22/1985;
DESCRIPTION: "This program lets you use your CP/M-80-based computer
to assemble code for the Motorola 6800, 6801, 6802,
6803, 6808, and 68701 microprocessors. The program is
written in BDS C for the best possible performance on
8-bit machines. All assembler features are supported
except relocation, linkage, listing control, and
macros.";
KEYWORDS: Software Development, Assemblers, Cross-Assemblers,
Motorola, MC6800, MC6801;
SEE-ALSO: CUG149, 6801 Cross-Assembler (Portable);
SYSTEM: CP/M-80;
COMPILERS: BDS C;
WARNINGS: "This package is specifically tailored to CP/M-80
machines and the rather non-standard, but high-
performance BDS C compiler. For other environments,
use the portable version of this package on CUG149.";
AUTHORS: William C. Colley III;
*/
6800 Cross-assembler Rev. 2.6 Page 1
6800 Cross-assembler
Rev. 2.6
Copyright (c) 1980,83,84,85 William C. Colley, III
The Manual Such As It Is.
6800 Cross-assembler Rev. 2.6 Page 2
Index
1 Format of Cross-assembler Commands....................... 3
1.1 Command Strings..................................... 3
1.2 Options............................................. 3
1.3 Examples............................................ 3
2 Format of Cross-assembler Source Files................... 5
2.1 Statements......................................... 5
2.2 Symbols............................................ 5
2.3 Numeric Constants.................................. 6
2.4 Strings............................................ 6
3 Expression Evaluation.................................... 8
4 6800/6801 Instructions................................... 9
4.1 No Argument Group................................... 9
4.2 One Argument Group.................................. 9
4.3 Two Argument Group..................................10
4.4 Branch Group........................................10
4.5 Jump Group..........................................11
4.6 Stack Group.........................................11
4.7 Pointer Group.......................................11
4.8 On Direct-page Addressing...........................11
5 Pseudo-operations........................................13
5.1 END.................................................13
5.2 EQU.................................................13
5.3 FCB.................................................13
5.4 FCC.................................................13
5.5 FDB.................................................13
5.6 RMB.................................................14
5.7 Conditional Assembly................................14
5.8 ORG.................................................15
5.9 SET.................................................15
5.10 CPU.................................................15
6 Error Messages...........................................16
7 Assembler Abort Conditions...............................18
8 Compiling the Assembler..................................19
9 Final Comments...........................................21
6800 Cross-assembler Rev. 2.6 Page 3
1 Format of Cross-assembler Commands
1.1 Command Strings
To run the cross-assembler, type the following command line:
A>a68 filename options
filename: The name of the source input file is
filename.68h, the list can go to
filename.prn, and the hex file can go to
filename.hex.
options: See next section.
1.2 Options
The source file comes from the currently logged disk drive
unless it is redirected by putting the string "sd" in the
options field. s specifies the source file and d is a
device code from the following list:
a, b, c, d Disk drives.
- The currently logged in disk drive.
Lines of input containing errors will always be output to
the console device. If the full listing is desired, it must
be called for by putting the string "ld" in the options
field. l specifies list file and d is a device code as per
the source file, or one of the following:
x Console device.
y List device.
The hex file will not be output unless called for as per the
list file.
Options must be run together into a single string with no
embedded blanks.
1.3 Examples
A>a68 barf source -- a:barf.68h
list -- none.
hex -- none.
A>a68 barf sblxha source -- b:barf.68h
list -- con:
hex -- a:barf.hex
A>a68 barf ly source -- a:barf.68h
list -- lst:
hex -- none.
6800 Cross-assembler Rev. 2.6 Page 4
A>b:a68 barf sbh- source -- b:barf.68h
list -- none.
hex -- a:barf.hex
6800 Cross-assembler Rev. 2.6 Page 5
2 Format of Cross-assembler Source Files
Lines of source input are terminated with CR/LF pairs.
Internally, the character before the LF is discarded, so if
the CR is missing, the last character of the line will be
eaten up. The internal line buffer will hold a 120 charac-
ter line. This may be changed by altering the "#define
LINLEN 120" statement in a68.h and recompiling the cross-
assembler. Excess characters in the line are thrown out.
Lower case letters are converted to upper case in as few
places as possible. They are:
1) In opcodes,
2) In checking for keywords such as NOT, and
3) In command strings.
This means that "not", "NOT", "Not", etc. are all possible
spellings of the bitwise logical inversion operator. This
also means that "foo" and "FOO" are different symbols.
Watch this if you start encountering U errors of symbols
that you "know" you defined.
2.1 Statements
Source files input to the Cross-assembler consist of state-
ments of the form:
[label] [opcode] [arguments] [;comments.]
Labels are recognized by their beginning in column 1. If it
doesn't begin there, it is assumed to be an opcode. Labels
are assigned the current program counter value unless the
line's opcode is "EQU" or "SET".
Opcodes may be either processor instruction mnemonics or
pseudo-ops.
The arguments following the opcode will vary with the op-
code. In the case of opcodes such as "NOP", they may be
absent entirely.
Lines terminate with either a CR/LF pair or a semicolon that
is not embedded in a quoted string. Anything after a semi-
colon is ignored by the assembler, but will appear in the
listing. Note that a semicolon in column 1 will make the
entire line a comment.
2.2 Symbols
Symbols may be of any length, but only the first 8 charac-
ters are significant. This may be changed by changing the
"#define SYMLEN 8" statement in a68.h and recompiling the
6800 Cross-assembler Rev. 2.6 Page 6
assembler. Note that this increases the storage required by
the symbol table as each entry in the symbol table is
SYMLEN+2 bytes in length. The following characters are
legal in a symbol:
A-Z a-z ! & . : ? [ \ ] ^ _ `
{ | } ~ 0-9
Note that symbols may not begin with 0-9 as this would make
them impossible to distinguish from Intel format numbers.
A special symbol * is always equal to the address of the
first byte of code generated by a given line.
2.3 Numeric Constants
Numbers begin with 0-9, %, @, or $. %, @, and $ are leading
base designators for binary, octal, and hexadecimal respec-
tively. If the number begins with 0-9, the assembler looks
for one of the trailing base designators B, O, Q, D, or H.
If the number does not end with one of these, it is assumed
to be decimal. B is the base designator for binary, O and Q
are for octal, D is for decimal, and H is for hexidecimal.
Trailing base designators and the hex digits A-F can be in
either upper or lower case. Note that hex numbers that
start with A-F and are specified with the designator H must
have a leading zero added to keep them from being mistaken
for symbols. For example:
$ff80 and 0ff80h evaluate to ff80 hex.
128 and 128d evaluate to 80 hex.
@035, 35o, and 35q evaluate to 1d hex.
%0111000 and 0111000b evaluate to 39 hex.
A character constant is a string composed of zero, one, or
two ASCII characters, delimited by either single or double
quotes (' or "). Note that single quotes only balance
single quotes, and double quotes only balance double quotes.
Thus a character constant of 22 hex can be specified by '"'.
For example:
"ab" evaluates to 6162 hex.
"" evaluates to 0000 hex.
"'" evaluates to 0027 hex.
'A' evaluates to 0041 hex.
Note that in the two-character character constant, the left-
hand character will appear in the upper-order byte and the
right-hand character will appear in the lower-order byte.
2.4 Strings
Strings are formed in the same way as character constants
except that they may be of any length up to and including
255 characters. The first character will be placed in the
6800 Cross-assembler Rev. 2.6 Page 7
lowest-order memory byte. A line-feed character may not be
embedded in a string as it terminates the line and will
yield a quote imbalance error. Note that strings are only
valid in the arguement field of an "FCC" pseudo-op.
6800 Cross-assembler Rev. 2.6 Page 8
3 Expression Evaluation
The following operators are allowed in expressions. The
operators are listed in order of precedence.
Unary Plus, Unary Minus
*, /, MOD, SHL, SHR
+, -
>, >=, <, <=, <>, =
(These can also be written as GT, GE, LT, LE, NE,
EQ.)
NOT (1's complement)
AND (Bitwise logical AND)
OR, XOR (Bitwise logical OR and Exclusive OR)
HIGH, LOW
Parentheses are used to change the order of precedence.
During evaluation of an expression, as soon as a new opera-
tor is encountered that has precedence less than or equal to
the last operator encountered, all operations up to the new
operator are performed. That is, subexpressions involving
operators of higher precedence are computed first.
All operators except +, -, *, /, =, <>, >=, <=, >, < must be
separated from their operands by at least one space or tab.
The "HIGH mumble" is equivalent to "mumble SHR 8" and "LOW
mumble" is equivalent to "mumble AND $ff".
The relational operators (=, >, etc.) evaluate to $ffff if
the relationship is true, 0 if it is false.
Expressions are terminated by commas, semicolons, or CR/LF
pairs.
6800 Cross-assembler Rev. 2.6 Page 9
4 6800/6801 Instructions
The instructions of the 6800 and 6801 microprocessors fall
into several catagories. Each requires a certain set of
arguments and disallows all other arguments. Arguments may
be specified in any order and are separated by commas except
for the register specifiers A, B, and X which may be fol-
lowed by spaces or tabs. In addition, the register speci-
fiers A and B can be attached to the end of the opcode
mnemonic with no intervening separator character. The imme-
diate addressing mode is specified by prefixing an expres-
sion with a # sign. Blanks may be used freely throughout
the argument field (except within symbols or operators such
as NOT) to enhance the readability of the source code. The
basic syntax is as follows:
[label] LDA A,X,expression ;The A X and expression
;can be mixed up in any
;order.
[label] LDAA X,expression ;Here, the A register
;specifier is attached
;to the opcode.
4.1 No Argument Group
This group contains the following opcodes:
ABA ABX * ASLD * CBA CLC
CLI CLV DAA DES DEX
INS INX LSLD * LSRD * MUL *
NOP PSHX * PULX * RTI RTS
SBA SEC SEI SEV SWI
TAB TAP TBA TPA TSX
TXS WAI
* = 6801 only
These opcodes permit no arguments.
4.2 One Argument Group
This group contains the following opcodes:
ASL ASR CLR COM DEC
INC LSL * LSR NEG ROL
ROR TST
* = synonym for ASL
This group requires one argument from the following list:
1) A
2) B
6800 Cross-assembler Rev. 2.6 Page 10
3) X
X,expression
X expression
expression,X
4) expression
4.3 Two Argument Group
This group contains the following opcodes:
ADC ADD BIT CMP EOR
LDA ORA SBC SUB
This group requires an argument from each of the following
lists:
List 1:
1) A
2) B
List 2:
1) X
X expression
X,expression
expression,X
2) expression
3) #expression (Not valid for STA.)
(Note that this value must be
in the range -128 to 255.)
4.4 Branch Group
This group contains the following opcodes:
BCC BCS BEQ BGE BGT
BHI BHS * BLE BLO ** BLS
BLT BMI BNE BPL BRA
BRN *** BSR BVC BVS
* = synonym for BCC
** = synonym for BCS
*** = 6801 only
This group requires an expression as its argument. The
expression evaluates to the address that the branch is
attempting to reach. The destination address can be -128 to
+127 bytes from the address of the NEXT instruction. If
this distance is exceeded, the assembler will flag an error.
6800 Cross-assembler Rev. 2.6 Page 11
4.5 Jump Group
This group contains the following opcodes:
JMP JSR
This group requires an argument from the following list:
1) X
X expression
X,expression
expression,X
2) expression
4.6 Stack Group
This group contains the following opcodes:
PSH PUL
This group requires an argument from the following list:
1) A
2) B
4.7 Pointer Group
This group contains the following opcodes:
ADDD * CPX LDD * LDS LDX
STD * STS STX SUBD *
* = 6801 only
This group requires an argument from the following list:
1) X
X expression
X,expression
expression,X
2) expression
3) #expression (Not valid for STD, STS, STX.)
4.8 On Direct-page Addressing
The assembler will select the shorter direct-page addressing
in preference to the longer extended addressing if the
expression in the argument field meets the following qual-
ifications:
1) It contains no forward references. Note that
6800 Cross-assembler Rev. 2.6 Page 12
direct-page RAM definitions should be at the be-
ginning of the program.
2) It contains no evaluation errors such as undefined
symbols.
3) It evaluates to a quantity in the range 0-255.
6800 Cross-assembler Rev. 2.6 Page 13
5 Pseudo-operations
5.1 END
When this statement is encountered, the assembler decides
that the end of the source file has been reached. If this
statement is missing or in a conditional assembly block that
is not being assembled, the assembler will encounter end-of-
file on the source file. In this case, the assembler will
attach an END statement and will flag an error. The syntax
is as follows:
[label] END
If any IF statement is not closed with an ENDI at this
point, an error will be flagged.
This statement permits no arguments.
5.2 EQU
This statement is used to assign a permanent value to a
symbol. This value may not be subsequently changed by a
SET, another EQU, or by writing the symbol in column 1 as a
label. The syntax is as follows:
label EQU expression
A phasing (P) error will result if any forward references
are encountered in the evaluation of the expression.
5.3 FCB
This statement is used to place bytes in memory. Each byte
is defined by an expression. Multiple bytes can be defined
by expressions separated by commas. If an expression eval-
uates to a quantity outside the range -128 to 255, an error
is flagged. The syntax is as follows:
[label] FCB [expr1][,epxr2].....
5.4 FCC
This statement is used to place strings in memory. Its
arguments may only be strings. Multiple strings may be
placed in memory if the strings are separated by commas.
The syntax is as follows:
[label] FCC [string][,string].....
5.5 FDB
This statement is used to place words in memory. Each word
is defined by an expression. Multiple words may be defined
by expressions separated by commas. Words are placed in
6800 Cross-assembler Rev. 2.6 Page 14
memory with their high-order byte in the low-order memory
location and the low-order byte in the high-order memory
location. The syntax is as follows:
[label] FDB [expr1][,expr2].....
5.6 RMB
This statement is used to reserve a block of memory for
working storage, etc. It requires one argument that gives
the number of bytes of storage to reserve. The syntax is as
follows:
[label] RMB expression
5.7 Conditional Assembly
Blocks of code can be assembled or not assembled based on
the value of some expression. The basic syntax is as fol-
lows:
IF expression
(lines of code)
ENDI
If the expression evaluates to 0, the code will not be
assembled. The source lines will be transfered to the
listing, but no hex output will be generated.
In addition, the ELSE directive is supported as follows:
IF expression
(lines of code)
ELSE
(more lines of code)
ENDI
This is equivalent to:
IF expression <> 0
(lines of code)
ENDI
IF expression = 0
(more lines of code)
ENDI
6800 Cross-assembler Rev. 2.6 Page 15
Note that labels are not permitted on conditional assembly
directives. Also note that an END statement can fail to be
recognized if it is in a conditional assembly block with a
false expression.
A phasing (P) error will be flagged if there are any forward
references in the expression.
5.8 ORG
This statement is used to load a value into the assembly
program counter. The value is obtained from the expression.
If the expression contains forward references, a phasing (P)
error will result. If a label is present, it will be EQUed
to the new program counter value. The syntax is:
[label] ORG expression
5.9 SET
This statement is used to assign a temporary value to a
symbol. The symbol may not be redefined by an EQU or by
writing it in column 1 as a label, but it may be redefined
by another SET statement. The value for the symbol is
obtained from the expression. If it contains forward refer-
ences, a phasing (P) error will result. The syntax is:
label SET expression
5.10 CPU
This statement turns the 6801 opcodes on or off. If the
required expression evaluates to 6800 (decimal), the 6801
opcodes are turned off. If it evaluates to 6801, the 6801
opcodes are turned on. Otherwise, a value (V) error is
flagged. If the expression contains any forward references,
a phasing (P) error results. If a 6801 opcode is encoun-
tered while the 6801 opcodes are turned off, an opcode (O)
error results. The syntax is:
[label] CPU expression
6800 Cross-assembler Rev. 2.6 Page 16
6 Error Messages
Error messages are flagged with a single letter in column 1
of the offending line in the listing. The meaning of each
letter follows.
A The addressing mode specified (X, #) is illegal in
this instruction.
B Distance on a branch instruction is too great.
Use a jump instruction with a branch around it, or
rearrange your code to shorten the distance.
D Digit too large for the base was encountered. In
particular, watch for 8 or 9 in an octal number
and A-F in a decimal number.
E Expression ill-formed. Look for #, A, B, X embed-
ded in an expression or like flaws.
I If stack imbalance. Look for ELSE or ENDI without
an IF or an IF still open at the end of the file.
L Invalid label. Label may contain invalid charac-
ters or be equal to a reserved word like A or NOT.
Label may be present on a conditional assembly
directive.
M Label multiply defined. Label defined more than
once and all definitions are not SET statements.
O Invalid opcode. Look for misspellings, missing
semicolons, opcodes in column 1, or 6801 opcodes
with 6801 opcodes are turned off.
P Phasing error. Look for expressions in ORG, EQU,
SET, IF, or CPU directives that contain forward
references. If none exist, something wierd is
going on as a label that was defined in pass 1
mysteriously vanished in pass 2.
R A or B specified where not allowed or not speci-
fied where required.
S Syntax error. Check your syntax against my sam-
ples.
T Too many arguments on this line. FDB directives
may only define 127 words, while FCC and FCB
directives may only define 255 bytes. On other
statements, you put superfluous arguments on the
line.
U Undefined symbol encountered during expression
evaluation.
6800 Cross-assembler Rev. 2.6 Page 17
V Value out of bounds. In particular, FCB expres-
sions and 8-bit immediate values must evaluate to
-128 to 255, index values must evaluate to 0
to 255, and CPU arguments must evaluate to 6800 or
6801.
* This statement generated by the assembler. Right
now, this only happens if you drop an END state-
ment or remove it through conditional assembly.
" Quote imbalance error. Bear in mind that ' will
not terminate a string started with " and vice-
versa.
( Parenthesis imbalance error. Count them!
6800 Cross-assembler Rev. 2.6 Page 18
7 Assembler Abort Conditions
Under certain circumstances, this assembler will just give
up and quit in the middle of an assembly. If you don't get
the error count diagnostic on the console, read your screen
for sure! The following messages occur:
1) Can't open source.
The source file does not exist on the specified
disk drive.
2) Can't open list.
Can't open hex.
No directory entries left on the disk drive in
question.
3) Illegal command line.
No file info supplied.
Bone up on command lines.
4) If stack overflow.
IF directives may only be nested 16 deep. Rebuild
your source code to reduce your nesting depth, or
change the "#define IFDEPTH 16" statement in
a68.h and recompile the assembler.
5) Disk read error.
Source file has a bad CRC or some other difficul-
ty.
6) Disk write error.
Out of disk or directory space on the list or hex
file.
7) Error closing file.
Problem closing list or hex file. You shouldn't
get this one.
8) Symbol Table Overflow.
Your source program defines too many symbols. The
current limit is 500. If you have more memory
than I do, you can change the "#define SYMBOLS
500" line in a68.h and recompile the assembler.
Otherwise, you must work on your source code.
6800 Cross-assembler Rev. 2.6 Page 19
8 Compiling the Assembler
To compile the assembler as it stands, you will need the
following items:
1) 40K of RAM.
2) The BDS C Compiler Version 1.4x or 1.5x (good box,
Leor!!).
3) Digital Research's MAC macro assembler (BDS C 1.4x
only).
Note: Only needed if you want to play with
the functions in a68tbls.asm as they
exist in a form digestible by CLINK in
the file a68tbls.crl.
To get a68tbls.crl up from scratch with BDS C 1.4x, you do
the following. I assume everything lives on drive A.
A>b:mac a68tbls $pz sz
A>load a68tbls
A>era a68tbls.hex
A>era a68tbls.crl
A>ren a68tbls.crl=a68tbls.com
With BDS C 1.5x, you do the following. Again, I assume
everything lives on drive A.
A>casm a68tbls
A>asm a68tbls.aaz
A>ddt a68tbls.hex
-g0
A>save 8 a68tbls.crl
A>era a68tbls.hex
You should now have a68tbls.crl on drive A.
Now you are ready to compile the rest of the beast.
A>cc1 a68.c -e4700
A>cc1 a68asmln.c -e4700
A>cc1 a68eval.c -e4700
A>cc1 a68get.c -e4700
A>cc1 a68put.c -e4700
A>cc1 a68symb.c -e4700
Now you can link it all together.
A>clink a68 a68asmln a68eval a68get a68put <^E>
a68symb a68tbls -s
And, as if by magic, you've got a68.com!
6800 Cross-assembler Rev. 2.6 Page 20
Note that the linkage should all be done on one line, or bad
things may happen like inadvertent pulls from DEFF.CRL and
DEFF2.CRL.
Note that if you have more than 40K of RAM, you may want to
increase your symbol table size. Symbols are 10 bytes each,
so plan accordingly.
6800 Cross-assembler Rev. 2.6 Page 21
9 Final Comments
Happy assembling! If you have questions or note any bugs,
I'd appreciate a shout at (216)775-3680 after 1830 hrs.
Eastern time. The questions will point up weaknesses in the
manual, and the bugs need to be stamped upon unmercifully.
Page 20
Note that the linkage should
