PS/2 connector

From Wikipedia, the free encyclopedia

PS/2 connector
The color-coded PS/2 connection ports (purple for keyboards and green for mice).
Type	Keyboard and Computer mouse data connector
Production history
Designer	IBM
Designed	1987
Superseded	DIN connector and DE-9 connector
Superseded by	Universal Serial Bus
Specifications
Data signal	Serial data at 10 to 16 kHz with 1 stop bit, 1 start bit, 1 parity bit (odd)
Pins	6
Connector	Mini-DIN
Pin out
Female connector from the front
Pin 1	+DATA	Data
Pin 2	Reserved	Reserved*
Pin 3	GND	Ground
Pin 4	Vcc	+5 V DC at 100 mA
Pin 5	+CLK	Clock
Pin 6	Reserved	Reserved**
* On some laptops mouse data for splitter cable. ** On some laptops mouse clock for splitter cable.

The PS/2 connector is used for connecting a keyboard and a mouse to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987. The PS/2 mouse connector generally replaced the older DB-9 RS-232 "serial mouse" connector, while the keyboard connector replaced the larger 5-pin DIN used in the IBM PC/AT design. The keyboard and mouse interfaces are electrically similar with the main difference being that open collector outputs are required on both ends of the keyboard interface to allow bidirectional communication. Normal desktop motherboards will not identify the keyboard and mouse if they are placed on each other's sockets.

Laptops generally have a single port that supports either a keyboard or a mouse. Sometimes the port also allows one of the devices to be connected to the two normally unused pins in the connector to allow both to be connected at once through a special splitter cable. The mouse interface is somewhat different from RS-232 (which was generally used for mice on PCs without PS/2 ports) but nonetheless many mice were made that could operate on both with a simple wiring adaptor.

In the 386, 486 and Pentium era, the connectors were also seen on some PC clones with non-standard case designs and the PS/2 mouse connector was sometimes seen on a separate backplate on systems using a standard AT case. However PS/2 ports only became the norm much later with the introduction of the ATX form factor. The design decision for identical but incompatible connectors would prove aggravating to consumers. To help alleviate this, PS/2 keyboard and mouse connectors were later color-coded: purple for keyboards and green for mice as defined by the Microsoft PC 97 standard.

PS/2 mouse and keyboard connectors have also been used in non-PC compatible computer systems, such as the DEC AlphaStation line.

Today laptops and a large number of desktops do not include PS/2 ports and so the port is now regarded as a legacy interface, having been superseded by USB. Many current keyboards and mice support both USB and PS/2 with a simple wiring adaptor and active adaptors are available which plug into a USB port and provide a pair of PS/2 ports.

PS/2 ports are designed to connect the digital I/O lines of the microcontroller in the external device directly to the digital lines of the microcontroller on the motherboard. They are not designed to be hot swappable. Hot swapping PS/2 devices usually does not cause damage due to the fact that more modern microcontrollers tend to have more robust I/O lines built into them which are harder to damage, however, hot swapping can still potentially cause damage. Shorting one pin to another on a PS/2 port can easily kill one or both microcontrollers.