
          BANKSWITCHING FOR TheNet X1 ( TNC2 only )

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  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). NOTE - I am told that this is a typo. Pin 1 is not
ground but pin 10 is. It is likely therefore that pin 16 should
be connected to pin 10.

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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