The serial Keyboard used on Personal Computers [PCs] is a [PS/2] 6 pin Circular DIN.
The pin-out for the PS2 Keyboard or Mouse port is: Pin 1; Data, Pin 2; Reserved, Pin 3; Ground, Pin 4; +5 Vdc, Pin 5; Clock, Pin 6; Reserved.
Another variant called the AT Keyboard uses a 5-pin DIN; with Pin 1; Clock, Pin 2; Data, Pin 3; Reserved, Pin 4; Ground, Pin 5; +5 volts.
The AT style keyboard was developed before the PS2 Keyboard interface, so most keyboards found these days will be the PS2 variant.
However; most new computers ship with keyboards using USB ports to handle this function, Universal Serial Bus [USB].
In general both the Obsolete AT keyboard and out-dated PS/2 style keyboard connector will not be present on the newest PC's.
| PS2 Keyboard | AT Keyboard | ||
| Pin Number | Function | Pin Number | Function |
| 1 | Data | 1 | Clock |
| 2 | Reserved | 2 | Data |
| 3 | Ground | 3 | Reserved |
| 4 | 5 volt | 4 | Ground |
| 5 | Clock | 5 | 5 volt |
| 6 | Reserved | 6 | NC |
These Keyboard interfaces are serial interfaces, using just one data line. The protocol is just like the RS232 interface, 8-bits of data with both a start and stop bit.
The 5-pin or 6-pin keyboard interface is not electrically compatible with the RS232 [EIA232] interface,
but the same protocol is used in Personal Computers.
The data or keys are encoded using normal ASCII coding.
The motherboard keyboard interface uses open-collector lines pulled to 5 volts to drive the data and clock signals compatible with TTL signaling levels. A number of manufacturers produce Keyboard encoder ICs.
Mouse and Key Board Manufacturers
KVM Manufacturers
All other PC interfaces are listed on the Personal Computer Buses page.
Use the Equipment Icon below to navigate to additional PC gear manufacturers.
Engineering Key words: IBM, AT, PS2, Keyboard, Apple, Macintosh, MAC, Computer Buses,
Connector Pin-Outs,
Interface Standard, Specification, Spec,
Physical Interface, Description, Personal Computer Interface, Peripheral,
Printer Interface, Keyboard pinout, Obsolete, Out-dated, Legacy Equipment, Gear, Signal names.
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