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20 pin IDC male connector layout
20 pin IDC male connector
at the computer
Found on the Osborne 1 luggable computer, released by Osborne Computer Corporation in 1981. This pinout came from the Osborne 1 Technical Manual, and I have had a quick look at the PCB to check it.




 

Pin
Number
Pin
Name
Description
1 GND System ground/shielding
2 A4 Row/address line
3 A0 Row/address line
4 A3 Row/address line
5 A6 Row/address line
6 A2 Row/address line
7 A5 Row/address line
8 A1 Row/address line
9 A7 Row/address line
10 D0 Column/data line
11 D1 Column/data line
12 D2 Column/data line
13 D3 Column/data line
14 D4 Column/data line
15 D5 Column/data line
16 D6 Column/data line
17 D7 Column/data line
18 NC Exists in cable, not connected at either end
19 +12V Connected on PCB, not in cable
20 GND System ground/shielding

Pin 1 is towards the top-right when looking at the front of the computer in the usual fashion. On the later '1a' model which I have, the plug on the coiled keyboard cable actually has 24 holes but the outer 4 do not mate with pins (it's not quite the same plug you find on a ribbon cable).

The Osborne 1 keyboard contains no electronics and does not require a power supply. The row and column lines connect directly to a matrix of keys. I believe that to read a row, the address is selected such that exactly one of the row outputs is driven low. Any pressed keys in that row will cause a zero to be read on the respective column line, while other column lines will be pulled up.

Pins 2-9 are driven by the system address bus through open-collector inverters. Pins 10-17 are pulled up to the system +5V supply by a 3.3K resistor pack, and buffered onto the system data bus when the processor reads the keyboard.

Pin 19 can be connected to the system +12V supply through J6 (a 2-pin link, open on my Rev. D PCB) and R21 (22 ohms).

I'm intending to build a PS/2 keyboard adapter using an ATtiny and a bunch of 74LS374's, as my keyboard was busted when I got it (eBay bargain).

Keyboard matrix layout
  D0 D1 D2 D3 D4 D5 D6 D7
A0 Esc Tab Ctrl   Shift Return ' [ ]
A1 1 ! 2 @ 3 £ 4 $ 5 % 6 ^ 7 & 8 *
A5 Up Left 0 ) Space . > P O 9 (
A2 Q W E R T Y U I
A3 A S D F G H J K
A4 Z X C V B N M , <
A6 Right Down - _ / ? ; : \ | L = +
A7       Lock        




 

20 pin IDC female connector layout
20 pin IDC female connector
at the keyboard cable
According to 4 reports in our database (4 positive and 0 negative) this pinout should be correct.

Is this pinout
Source(s) of this and additional information: Osborne 1 Technical Manual
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