The "Serial Mouse" uses a RS-232 style interface with -5 to -12 VDC as logical "1" and +5 to +12 VDC as logical "0". The PS/2 mouse interface is a TTL-style interface, which uses 0 - +2 VDC as logical "0" and +3 - +5 VDC as logical "1".
In addition - and to make things worser - the RS-232 is an asynchronous interface, the PS/2 interface is a synchronous, where the data is sent along with a clock signal. It uses a simplified 4-wires serial interface with +5VDC (for the transceiver), GND, keyboard / mouse clock and keyboard / mouse data. The data and clock line can be used from the keyboard / mouse controller and the attached device as well following a particular handshake, which defines which is the active "sender" and which is the "receiver". So: it is not *that* easy conversing serial mouse to PS/2 and vice versa.
The "dual mode" mice have an automatic logic detection and sort of adaptive interface electronic, which detects whether the mouse is attached to a serial port or a PS/2 port and set the output drivers accordingly.
| Mini-DIN | D-SUB | ||
|---|---|---|---|
| +5V | 4 | 4+7+9 | DTR+RTS+RI |
| Data | 1 | 1 | CD |
| Gnd | 3 | 3+5 | TXD+GND |
| Clock | 5 | 6 | DSR |
