| 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| Superseded | DIN connector and DE-9 connector | |
| Superseded by | Universal Serial Bus | |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 | Not connected | Not connected* |
| Pin 3 | GND | Ground |
| Pin 4 | Vcc | +5 V DC at 275 mA |
| Pin 5 | +CLK | Clock |
| Pin 6 | Not connected | Not connected** |
| * On some laptops mouse data for splitter cable. ** On some laptops mouse clock for splitter cable. |
||
The PS/2 connector is used for connecting some keyboards and mice 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 DE-9 RS-232 "serial mouse" connector, while the PS/2 keyboard connector replaced the larger 5-pin DIN used in the IBM PC/AT design. The PS/2 designs on keyboard and mouse interfaces are electrically similar and employ the same communication protocol. However, a given system's keyboard and mouse port may not be interchangeable since the two devices use a different set of commands. Following the release of USB keyboards, PS/2 keyboards and mice have become less popular.
Contents |
Port availability
When IBM-compatible PCs widely used the 386 and 486 processors, 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 during 1993–1997. 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 PC 97 standard.
Old 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. This configuration is common on IBM/Lenovo Thinkpad notebooks among many others.
The PS/2 keyboard interface was electrically the same as the 5-pin AT system and keyboards designed for one can be connected to the other with a simple wiring adapter. The PS/2 mouse interface is substantially 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 adapter.
PS/2 mouse and keyboard connectors have also been used in non-IBM PC-compatible computer systems, such as the DEC AlphaStation line, early IBM RS/6000 CHRP machines and SGI Indy, Indigo 2, and newer (Octane etc.) computers.[1]
Legacy port status and USB
Today's laptops frequently do not include PS/2 ports and so the port is now regarded as a legacy port on Wintel, having been superseded by USB. Many current keyboards and mice support both USB and PS/2 with a simple wiring adapter and active adapters are available which plug into a USB port and provide a pair of PS/2 ports (active adapters in the other direction are very rare). PS/2 ports however, can still be found on modern desktop computer motherboards, although some newer motherboards have no PS/2-port or only the keyboard port. These PS/2 ports cause fewer problems when KVM switching with non-Wintel systems.
Color code
Original PS/2 connectors were black or had the same color as the connecting cable (mainly white). Later PC 99 color code was introduced. PC 99 made the keyboard port, and the plugs on compliant keyboards, purple; mouse ports and plugs were green. In the beginning, the color scheme was not consistent between vendors. Logitech used the color orange for the keyboard connector for a short period, but switched to purple soon. Today this code is still used on most PCs. The pinouts of the connectors are the same, but most computers will not recognize devices connected to the wrong connector.
| Color | Description | |
|---|---|---|
| Purple | Keyboard | |
| Green | Mouse | |
Wiring inside keyboard may vary, but for most standard keyboards, they are the same:
| Color | Description | |
|---|---|---|
| Green | +CLK | |
| White | Data | |
| Yellow | GND | |
| Red | Vcc | |
Hardware issues
Hotplugging
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 than those of older controllers; however, hot swapping can still potentially cause damage on older machines, or machines with less robust port implementations.
If they are hotswapped, the devices must be similar enough that the driver running on the host system recognizes, and can be used with the new device. Otherwise, the new device will not function properly. While this is seldom an issue with standard keyboard devices, the host system rarely recognizes the new device attached to the PS/2 mouse port. In practice most keyboards can be hotswapped but this should be avoided.
Durability
PS/2 connectors are not designed to be plugged in and out very often, which can easily lead to bent or broken pins. PS/2 connectors only insert in one direction and must be rotated correctly before attempting connection. Most but not all connectors include an arrow or flat section which is usually aligned to the right or top of the jack before being plugged in. The exact direction may vary on older or non-ATX computers and care should be taken to avoid damage or bent pins when connecting devices.
Fault isolation
As noted, in a standard implementation both PS/2 ports are usually controlled by a single microcontroller on the motherboard. This makes design and manufacturing extremely simple and cheap. However, a rare side effect of this design is that a malfunctioning device can cause the controller to become confused, resulting in both devices acting erratically. The resulting problems can be difficult to troubleshoot (e.g. a bad mouse can cause problems that appear to be the fault of the keyboard).
See also
References
- ^ Lenerz, Gerhard (7 November 2006). "Common Input Devices". Hardware. SGIstuff. http://sgistuff.g-lenerz.de/hardware/input.php. Retrieved 2007-03-14.
External links
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