                  BANKSWITCHING FOR TheNet X-1

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.

At  the  end  of these descriptions, is a  note  by  Al,  WB0YRQ, 
describing  how  to  modify  the  MFJ1270C.  My  thanks  for  the 
information.

If  you  receive  CQ magazine, I  would  recommend  the  detailed 
drawings and modifications published by Buck Rogers in his column 
for  clear  instructions on implementing  bankswitching  and  the 
deviation meter PCB.

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

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
_________________________________________________________________


To   modify  the  MFJ-1270C  for  use  with   X1J/TheNet   EPROMS 
follow these instructions:

You  must  complete  all  of  these  steps  in order for  Net/Rom 
firmware to function.
 
NOTE:  if  you are not using X1J firmware skip the first step and 
make sure that JP15 is set for 256k.

Step 1: Bend  pin  1 of 27c512 out so it will not  touch  socket, 
        then jumper pin 1 of 27c512 to pin 8 of MODEM header  J4. 
        (see X1J docs)
        
Step 2: Remove  U40. Add jumper from pin 16 to pin 1 (ground  pin 
        16)
        
Step 3: Remove JMP9 altogether  (no jumper on any pins)
        
Step 4: Cut JMPX "PAD" to prevent node from hearing itself
        
Step 5: Add  100ohm  resistors to R14 and R15 if not  already  in 
        place.
        
This  information  came  directly from MFJ and  I  have  used  it 
successfully. Hope this helps you.

73's de Al WB0YRQ @ NF0N.#NENE.NE.USA.NA
Akron, Iowa. 712-568-2810  GRID <EN12RT> 
TCP/IP 44.50.2.6
Internet: SCHEMMERAL@BVC.EDU
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