A serial mouse uses the standard RS-232 interface to communicate with a computer. While modern systems use USB or PS/2, legacy serial mice typically utilize a 9-pin (DE-9) or 25-pin (DB-25) D-subminiature connector. Common 9-Pin (DE-9) Pinout
Because standard serial ports were not originally designed to supply power to peripherals, one of the most ingenious aspects of the serial mouse pinout is how engineers utilized the control lines from the computer to "steal" power to run the mouse’s internal electronics. serial mouse pinout
The mouse sends data to the computer via . It does not use Pin 3 (TXD) except in rare bidirectional protocols. A serial mouse uses the standard RS-232 interface
| Pin Number | Signal Name | Direction | Description | | :--- | :--- | :--- | :--- | | | DCD (Data Carrier Detect) | Input | often used for power stealing. | | 2 | RXD (Receive Data) | Input | Primary Data Line. The mouse sends movement data to the PC here. | | 3 | TXD (Transmit Data) | Output | Often used as a voltage source (+V) to power the mouse. | | 4 | DTR (Data Terminal Ready) | Output | Power Source & Reset. Provides positive voltage; toggling this resets the mouse. | | 5 | GND (Signal Ground) | — | Common ground reference for all signals. | | 6 | DSR (Data Set Ready) | Input | Often used for power stealing. | | 7 | RTS (Request to Send) | Output | Power Source. Used to supply power to the mouse circuitry. | | 8 | CTS (Clear to Send) | Input | Sometimes used for power; often left unconnected in simple mice. | | 9 | RI (Ring Indicator) | Input | Rarely used in mice; sometimes used for power or ignored. | The mouse sends data to the computer via