Keyboard Connections

Updated 22nd May 2022

Unfortunately, not all keyboards are equal communicators. As technology has developed, protocols and connectors have continuously changed. Here is information about the most prominent protocols and connectors used at some point by IBM and family keyboards, as well some pinout diagrams and tables to help with keyboard conversion activities.

Main keyboard protocols Female connector pinouts Modular cable end-to-end mappings Mainboard header pinouts Cable wire colour coding keys Header to Soarer's microcontrollers mappings

Main keyboard protocols

Set 1

August 1981

The Set 1 (PC/XT) protocol was the original PC scancodes effectively introduced by the IBM Personal Computer (5150) and subsequently used for the IBM Portable Personal Computer (5155) and IBM Personal Computer XT (5160). Modern PCs are largely incompatible with interfacing directly with Set 1/XT keyboards despite raw XT codes still technically supported by legacy BIOS and operating systems.

Set 3

October 1983

The Set 3 protocol was introduced with the IBM 3270 PC (a PC-based IBM 3270 terminal emulator), largely remaining unique amongst IBM's terminals for the '80s and '90s. Whilst later PS/2 keyboards should be compliant with Set 3, PCs then and now rarely had native support for this protocol. Even on the 3270 PC, an add-on card and BIOS extension were needed to translate the keyboard's scancodes back into Set 1/XT for the base PC to understand it.

Set 2

August 1984 (AT), April 1987 (PS/2)

The retroactively-named Set 2 (PC/AT) protocol was initially a subset of Set 3 introduced with the IBM Personal Computer AT (5170). A marked improvement over Set 1/XT, Set 2/AT allows commands to be received by the keyboard, making features like lock-lights possible. Set 2 was later extended into PS/2 with the launch of its namesake family of computers - the IBM Personal System/2. As differences began to appear between IBM's terminals and PCs, Set 2 and Set 3 eventually ended up with different scancodes for new key additions such as Windows keys during the late-'90s.

HID

January 1996

The Universal Serial Bus (USB) Human Interface Device (HID) class is an industry-standard specification dictating how computer peripherals such as keyboards operate, effectively ending the need for the three IBM Set scancodes. All USB keyboards prescribe to HID and it has supplanted PS/2 in everything except legacy computing and scenarios that require keyboard-based interrupts instead of the host computer polling the keyboard (as what happens with USB communication). Some USB keyboards can support outputting PS/2 scancodes, however, making a simple passive adapter possible.

Female connector pinouts

These are pinout diagrams for various IBM keyboard's connectors as they appear on either the computer-side or keyboard-side (if modular) sockets.

Host-side socket pinouts

XT/AT 180° DIN

5155 XT modular-6P5C ("RJ-25" like)

Terminal 240° DIN

Terminal modular-8P5C ("RJ-45" like)

PS/2 6-pin mini-DIN

Keyboard & mouse combo IBM keypad PS/2-like 6-pin mini-DIN

Apple Newton MessagePad X0044 8-pin mini-DIN

Device-side socket pinouts

Standard Model M SDL

Keyboard & mouse combo Model M3 modular-8P7C ("RJ-45" like)

Keyboard & mouse combo Model M4-1/M5-1/M5-2 SDL

Retail POS Model M7/M8/M9/M11 PS/2 SDL

Retail POS Model M7/M7-1/M8/M9/M11 USB 4x1 IDC

Modular POS Model M-e USB & PS/2 6x2 IDC

Modular cable end-to-end mappings

These tables describe the pin translation between one end of a modular keyboard cable to another (in all present cases, a form of SDL to PS/2).

6-pin SDL to single PS/2 (eg, standard Model M cable)

N/C

DATA

GND

CLOCK

+5V

N/C

6-pin SDL to dual PS/2 (eg, Model M4-1, M5-1 & M5-2 cable)

Mouse

CLOCK (mouse)

Keyboard

DATA (keyboard)

Both

GND

Keyboard

CLOCK (keyboard)

Both

+5V

Mouse

DATA (mouse)

8-pin SDL to PS/2 (eg, P/N 42M599 Model M7, M8, M9 and M11 cable)

CLOCK

GND

+5V

GND

+5V

DATA

Mainboard header pinouts

The following diagrams detail what the pins on the keyboard's logic/controller board do. The help with orientation, a solid white filled-in block represents clip location, empty boxes represent absent pins, and a small number in the top-left corner state the pin number as described in the keyboard's or host system's hardware maintenance manual. However, if all three of these are absent, orientation will instead be described. Additionally, a block with just an "X" inside denote an unused but present pin.

Type 1 IBM 5150 Model F

Clock

Data

GND

Reset

+5V

Type 2 IBM 5150/5155/5160 XT Model F

Clock

Data

GND

+5V

IBM 104-key "unsaver", 122-key and 5170 AT Model F, and 122-key Model M

+5V

Clock

GND

Data

Lexmark or Unicomp 101/102-key fixed cable PS/2 Model M

+5V

Clock

GND

Data

IBM 5291 Model F

Orientation: position the host board as such that this header is to the left side of said board.

Count 64

Count 32

Count 16

Count 8

Count 4

Count 2

Key Down

GND

+5V

Count 1

GND

Strobe

GND

P/N 69H8533 IBM 5535-ZPP numeric keypad

Key: M denotes a mouse pin and K denotes a keyboard pin.

1: DATA (M)

2: DATA (K)

3: GND

4: +5V

5: CLOCK (M)

6: CLOCK (K)

Cable wire colour coding keys

The following tables show what header and plug pins the colour-coded wires inside IBM and family keyboard cables lead to. Note that having a third-party cable on your keyboard is possible, so if you're not sure about if the cable is original or not, you can double-check the colour coding yourself by observing what header pins the individual coloured wires connect to.

IBM 5150/5155/5160 XT Model F

Brown

+5V

Red

GND

White

Data

Black

Clock

Silver

N/A (grounding screw)

Lexmark 101/102-key fixed cable PS/2 Model M

Black

+5V

Red

Clock

White

GND

Yellow

Data

Silver

N/A (grounding screw)

P/N 69H8533 IBM 5535-ZPP numeric keypad

Yellow

Green

Blue

Red

White

Black

Header to Soarer's microcontrollers mappings

The following tables describe how you can connect various microcontrollers (currently Teensy 2.0, Arduino Micro and Pro Micro) to the headers of various IBM keyboard's mainboards as a part of a USB conversion process. These have only be tested to work for Soarer's Converter and Controller active converters, although they may be of use on other types of converters too. Please see the various diagrams above for a visual representation of the keyboard headers.

IBM XT, AT, 104-key "unsaver" and 122-key Model F, and 101/102 and 122-key Model M

+5V

VCC

+5V

VCC

GND

Data

D3 (SCL)

Clock

D2 (SDA)

IBM 5291 Model F

Note that this keyboard's header pinout has three GND pins - you only need to use one of the pins and you're free to use any one of them.

Count 2

SCK

Count 4

MOSI

Count 8

MISO

Count 16

Count 32

Count 64

D10

Key Down

D3 (SCL)

GND

+5V

VCC

+5V

VCC

Count 1

RXLED

Strobe

D2 (SDA)

Sources & contributors

KbdBabel - data on most keyboard connectors TheMK#1822 - PS/2 pin positions for Modular POS Model M-e 6x2 IDC pinout diagram

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