A PS/2-to-serial mouse adapter is a purely passive wiring cable with no active circuitry. It connects a mouse fitted with a 6-pin mini-DIN (PS/2) plug to a host computer’s DE-9 RS-232 serial port. The PS/2 mouse interface was introduced by IBM with the Personal System/2 family in 1987, using a bidirectional synchronous serial protocol at TTL levels over an open-collector bus. The RS-232 serial mouse protocol uses Microsoft-compatible 3-byte movement packets transmitted at 1200 baud. Because the adapter contains no conversion logic, it functions only with a combo mouse — a device that detects its host interface at power-on and switches protocol accordingly.
6 PIN MINI-DIN FEMALE to the mouse
9 PIN D-SUB FEMALE to the computer
| Mini-DIN | D-SUB |
|---|---|
| GND | 3 |
| RxD | 2 |
| TxD | 6 |
| +5V | 4 |
Signals
- GND — Signal ground; common reference for both interfaces.
- RxD — Received Data on the DE-9 side (pin 2); carries mouse movement and button data from the device to the host at 1200 baud.
- TxD — Transmitted Data on the DE-9 side (pin 6); carries host-to-device commands (used by some mice for rate/resolution configuration).
- +5V — Supply voltage from the PS/2 port; the serial mouse draws power internally from the RS-232 RTS line rather than this pin when operating in serial mode.
Notes
The adapter is passive — it contains no voltage-conversion or protocol-translation circuitry. It will not function with a standard PS/2-only mouse connected to a serial port, nor with a standard serial-only mouse connected to a PS/2 port. The PS/2 interface operates at TTL logic levels (0 V / +5 V) over an open-collector clock and data bus; the RS-232 interface operates at ±12 V levels. A combo mouse contains its own internal level-conversion circuitry and selects the active protocol by sensing the electrical characteristics of the connected port at power-on. The serial mouse protocol (Microsoft format) uses 1200 bps, 7 data bits, no explicit parity, and transmits 3-byte movement packets via RxD, RTS, and Signal Ground; the mouse derives its operating power from the RTS line through an on-board 5 V conversion circuit.
References
- IBM PS/2 Hardware Interface Technical Reference: Common Interfaces (October 1990)
- IBM Personal System/2 Hardware Interface Technical Reference (May 1988)
- TrackPoint Engineering Specification Version 4.0 — Serial Supplement (IBM, 1998)
- AN519: Implementing a Simple Serial Mouse Controller (Microchip Technology, DS00519C)