have talked about the CP-1252/ASN-128 before Hacking The Navigation Computer Display. I have changed my mind about using a ps2 decoder to interface with the keyboard. I will write my own. It's about 30 lines of code, not including Scanner.h  (prototypes) and Matrix.h which describes the 2 dimension array for the keyboard.

The Switches where made by Clare Pendar (Now Visualux) Pn: S180 11D5F4 and are very pricey. Thankfully I have about 3 of these units in various stages of disrepair so parts thankfully are not an issue.

Analysis: The Keyboard consists of 14 STDP switches, they also have a light keycap. They are arranged in three columns where the outside columns have 5 switches each and the middle column has 4. Each switch has pins 1 and 2 jumpered together forming an SPDT switch.

ConnectorGoes To:
W5P2Thumb Wheel Switch 1
W5P3DISPLAY Switch 1
W5P5Thumb Wheel Switch 2
W5P8Relay - Remove
W5P9MODE Switch 2
ConnectorPincolorGoes To:
W5P112yellow0, 1, 2, 3
W5P114yellowENT, CLR, KBD
W5P411yellow4, 5, 6, 7
W5P412yellow8, 9, TGT
  • First I used a DVM to check which yellow wire went where, as you can see in the table below.
  • But the blues where a mess but junk box comes to the rescue. I had remains of an old project that had some led mounted on a header connected to a resistor pack. Now this will do. So I just connected the 4 LEDs to the blue wires on the two connectors (W5P1 & W5P4) and put 5 volts and the rest is history, as you see the table below.

This is the first cut off my keyboard scanner as you can see I have not included anything for de-bounce, etc. if scan() returns an alphanumeric character we are good to go. If scan() returns -1 then nothing there.


PS give a break with the code I know there are some errors here but you get the idea.




*  CP-1252.scan.c


*  Created on: Oct 16, 2018

*      Author: Harrison



#include "Scanner.h"

#include "Maxtrix.h"


char scan () {

   int state;

   char varchar = -1;

   int row =1;

   int col;


// Start rows in known state

   for (row = 1; row < 5; row++) {

      digitalWrite( row, HIGH);}


// Seach for a row + col

   do {

       for ( col=1; col <=4; col++ ) {

           if ((state = digitalRead(col)) == HIGH) {


           else {

                varchar = Matrix[row][col];


   while( row < 5 );

retrun( varchar);