BANKSWITCHING FOR TheNet X1

What   follows   is two versions of how to  do  the   bankswitching.  Saying 
things in two different ways is a neat way of making  sure that  ambiguities 
are  exposed, so here goes. The first version  is by me, the second  by  Bob 
G8HBE.

=========================================================================

For  the  reduced TNC2 version, the instructions  are  simply  as follows :

1.   Bend out pin 1 of the EPROM so that when inserted  into the  socket  it 
     will not contact pin 1 of the socket  or any other pin.

2.   Connect  a wire from the SIO-0 DTRA pin ( pin 16  )  to the  bent   out  
     pin  ( pin 1 ) of the  eprom.  The  DTRA signal  should also appear  on 
     pin 8 of the  TAPR  modem disconnect header.

The  status  led will flicker as it now shows the  state  of  the bankswitch 
signal.

One   word  of caution - if you can, just check the signal on pin 1  of  the 
eprom  - make sure it switches fast and cleanly - i suspect that if it  does 
not, errors will occur.

=========================================================================

                                                            Robert Smith
                                                        38 Norris Close,
                                                              Chiseldon,
                                                              Nr Swidon,
                                                              Wiltshire.
                                                                 SN4 0LR

                                                          6 October 1991

BANKSWITCHING for TheNet X1

So   that  the  27C512 does not get damaged by the bending  of  pin   1  and  
soldering   it  I have made the modification to  the  TNC-200,  Tiny  2  and 
MFJ1274 type TNC's as follows.

To  modify your TNC you will require a piece of  thin  connecting wire about 
100  mm  long  and a 28 pin IC socket,  you may also need a  little  bit  of 
inserlating tap.

Before starting the modification make sure that power to the  TNC has   been 
disconnected and that the lithium battery link as  been removed.

Remove the 27C256, U23 in a MFJ1274/TNC200 or U2 on a Tiny 2  and put it  in 
a safe place.

Taking your New 28 pin IC socket, bend pin 1 outwards and  solder the end of 
the wire to the bent out pin.

Plug   the   IC socket into the socket you took  the  27C256   from,  making 
sure that you plug it in the correct way round.

Depending  on  the type of IC socket that is mounted  on  the  PC board  you 
may find that pin 1 on both IC sockets may touch,   if this seems to be  the 
case put a little pieces of inserlating  tap between them.

Also on the Tiny 2 make sure that the bent pin does not touch the CPU chip.

Now  connect the other end of the wire to pin 16 on the  Z80  SIO chip.

This   signal  can also be found on pin 8 of the  modem   disconnect  header 
which is J5 on a Tiny 2, also the same signal can be found on  pin  5  of U6 
(74HC14) on the Tiny 2. On  a  TNC200  you  can connect the wire to the side 
of  R51  nearest U23, this is just  20 mm from pin 1 of U23  on  the  TNC200 
board.

If  in doubt use a test meter and check the continuity from pin 16  on   the 
Z80 SIO chip to the point where you are going  to  solder the wire.

Once   you  have  done this you can plug the new   27C512   Programmed  with 
TheNet X into the new mounted IC sockets.

Re-insert  the  lithium battery link, Connect your computer  to   the  RS232  
socket,   12   volts to the TNC and switch  on,  if  all  is  working   well  
the  the  STA light will be flickering and  after  a second a  message  will 
appear on you screen.

Modification complete.
G8HBE    6-Oct-91