KBD-Reset V1.02 (25 Nov 1996)
            -----------------------------

 The problem:

   Many users have equiped their Amiga 1200 with a bigger tower-case.
   Some of them may want to use an A2/3/4000 keyboard.

   This doesn't seem to make any problems, and the connection can be done
   without electronic constructions. However, the reset-key-combination
   (Amiga-Amiga-Ctrl) won't work.


 The soultion:

  My circuit. This one works fine with my configuration (A1200/Eagle-Tower/
  A4000 keyboard).


 Circuit
 -------

  +-----------------+
  | Amiga keyboard  |
  +-----------------+
      |   |                KBDDATA
      |   +-------------------------------+
      |                                   |
      |                    KBDCLK       +-------------------+
      +---------------------------------| A1200 motherboard |
      |                                 +-------------------+
  +-----------------+      KBDRESET       |
  | my circuit      |---------------------+
  +-----------------+
      |
        / ext.
       /  reset
      |
     -+-

(+5V power and Gnd are not mentioned here.)



         +5V
          |
         | | 100k
         | |          Ge-Diode
          |    |\               ____          |\           |\
KBDCLK >--+----| o--+---|<|-----____----+-----| o----------| \    |\
 (IN)          |/   |  ____       1k    |     |/           |  o---| o--> KBDRES
                    +--____-------------+        +-----+---| /    |/     (OUT)
                        33k             |        |     |   |/
                                      __|__+    | |10k   / external
                                 22uF _____     | |     /  reset switch
                                        |        |     |
                                      --+--      o   --+--
                                                +5V

part list
---------

1* 74HCT132 (quardruple schmitt NAND gate)
1* 22uF (electolytic capicator)
1* 1K
1* 10k
1* 100K
1* 33k (Adjust)
1* Germanium Diode
1* switch (1*on), if needed

Circuit diagram 74HCT132            DIL 14 case, viewed from above
------------------------            ------------------------------

   1----|\                              +----o----+
        | o---- 3                    1--|         |--14
   2----|/                            --|         |--
                                      --|  74HCT  |--
                                      --|   132   |--
   4----|\                            --|         |--
        | o---- 6                     --|         |--
   5----|/                           7--|         |--8
                                        +---------+

   9----|\
        | o---- 8
  10----|/


  12----|\
        | o---- 11
  13----|/

 Pin 7  = GND
 Pin 14 = +5V



Comments
--------

The 74HCT132 is a high-speed CMOS-chip. This one cannot be replaced by a
74132 or 74LS132 !

The external reset-button is optional. If it isn't needed, You may want
to leave it away.

I use a germaniumdiode, to unload the electrolytic capicator as deep as possible.
If this one isn't available, You can also use a 1N4148 or any other siliziumdiode.
Remember that this will change the timing behaviour of the circuit.

If the circuit does not work properly (due to component tolerances), You can
try to change the 33KOhm Resistor, which is marked with "ADJUST" in the          
parts list, into a smaller one.

The A2000 and A3000 keyboards are the same. The only change regarding the
A4000 is that its keyboard has a mini-DIN-plug instead of the standard 5-pin
plug. However, all of these keyboards will work with the A1200.


Connecting to the A1200 motherboard
-----------------------------------

(The following data has been taken out of the archive "1200ExKb.lha"
from Aminet-CD 5, found in directory "hard/hack").


                                |||||||||||
                              -+-----------+-
                              -|           |-
                              -|           |-
                              -|   8520PL  |-
                              -|           |-
                              -|     U7    |-
                              -|           |-
                              -|           |-
                              -|           |-
                              -|     ^     |-
                              -+-----------+-
                                |||||||||||
                                   ||
                                   | \KBDat (solder the lead here)
        |||||||||||                |
      -+-----------+-               \KBClk (solder the lead here)
      -|           |-
      -|           |-
      -| Keyboard  |---KBClk (solder here and bend pin up)              Floppy
      -|  Micro.   |---KBDat (solder here and bend pin up)              Power
      -|           |-
      -|    U13    |-                                                   oooo
      -|           |-               To                                  ||
      -|           |-              front                                ||
   /---|     ^     |-               of             ====>             +5v/|
   |  -+-----------+-             machine                                |
   |    |||||||||||                 ||     (power for the                |
   |                                ||     keyboard and my           Gnd /
   \_KBReset (solder the lead here) ||     circuit)
                                    ||
                                    \/


Here is a connection table of some Amiga keyboards:
---------------------------------------------------

A1000: (Connector on back of keyboard itself)

        (female)                +------+
                                | |||| |        1=Gnd
                                | 1234 |        2=KBClk
                                |      |        3=KBDat
                                +-+  +-+        4=+5v
                                  +  +
                                   ++

A2000/3000:

        (female)                  -v-
                                 /   \
                                |3   1|         1=KBClk
                                | 5 4 |         2=KBDat
                                |  2  |         3=unused
                                 \___/          4=Gnd
                                                5=+5v

A4000:

       (female)
                                  -v-
                                 / V \
                                |6   5|         1=KBDat
                                |4   3|         2=unused
                                | 2 1 |         3=Gnd
                                 \___/          4=+5v
                                                5=KBClk
                                                6=unused



This "hack" is mailware!
------------------------

If anyone tried to build it and succeeded, please send an E-mail to:

M.SCHULZ@FREEWAY.SHNET.ORG

Please tell me where You use the circuit. Thank You.

If You after all don't succeed, I may (no guarantee) build it for You,
please contact me at the above adress. Of course, anyone with questions
or comments can write to me, too.