11. Cables, extensions and adaptors The only wires needed in a mouse cable are as follows: TxD and RxD for data transfer, RTS and/or DTR for power sources, and ground. Translated into pin numbers, they are: 9-pin port 25-pin port TxD 3 2 RxD 2 3 RTS 7 4 DTR 4 20 Gnd 5 7 The above table may be of use if you wish to make adaptors between 9- and 25-pin plugs, or extension cables.