Paxon keyboard and functionality for other MSX?

By popolon_

Resident (62)

popolon_'s picture

30-10-2020, 08:21

Hi!

I have MSX paxon keyboards (PCK-50), and I am thinking to use it as NTT captain keyboard. Paxon keyboard connector has 22 pins, and it is strange that there is no +5V and no GND pins at all. Only X0-X7,Y0-Y8, and CAPS L,CAPS R,KANA L,KANA R pins. So CAPS and CANA leds are getting power via these own pins, no GND and +5V pins. And CAPS and KANA pins neither are connected to GND ( at least 1k2 Ohm resistance to GND). So how can the keyboard itself can work and detect key presses without GND pin?
The pin assignement is (looking into female keyboard connector)

---------------------------------
|22 21 20 19 18 17 16 15 14 13 12 | <---cable side---
|1  2  3  4  5  6  7  8  9  10 11 | 
---------------------------------

1 = Y2
2= Y3
3= X5
4= Y5
5= Y4
6= X1
7= Y0
8= Y1
9= X0
10= X3
11= Y6
12= X2
13= Y7
14= X4
15= X6
16= Y8
17= X7
18= KANA/L (10kohm to 5V line, 10kohm to GND line)
19= KANA/R (10kohm to 5V line, 1k2 ohm to GND line)
20= NC (but there is wire connected inside keyboard cable, in keyboard pcb and in plug side, but no traces is connected it to however inside keyboard)
21= CAPS/L (10kohm to 5V line, 10kohm to GND line)
22= CAPS/R (10kohm to 5V line, 1k2 ohm to GND line)

In the Paxon mainboard (PCT-50 DLU-A) side there is 8255PPI chip, and X0-X7 are connected to straight to PBx lines. Y0-Y8 lines are however coming via SN74LS145N.

So would this keyboard work in captain without that ground, just by connecting 5v line to L or R and the other pin pair to CAPS/KANA line and all other pins to same pins as in captains X and Y lines? Yes, keyboard matrix may not be as same...but?

Login or register to post comments

By Pac

Guardian (5918)

Pac's picture

30-10-2020, 09:15

Maybe this related thread will help you:

https://www.msx.org/forum/msx-talk/general-discussion/compat...

By caro

Champion (507)

caro's picture

30-10-2020, 17:07

popolon_ wrote:

So how can the keyboard itself can work and detect key presses without GND pin?

GND provides an open collector of the SN74LS145N chip, and level 1, pulled to + 5V inputs X0 ... X7.