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 electrical 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.
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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