The OPC-478 cable interconnects your IC-R5, your Icom IC-A22E and your Icom IC-A3 to your PC. The OPC-478 cable has a 9-pin D-sub connector on one end, and a 3,5 mm jack plug on the other. The D-sub connector connects to a 9-pin serial port on your PC whereas the jack plug goes (originally) into the earphone socket of your IC-R10.
Inside the D-sub connector a small circuit is built that converts the TTL-level data on the IC-R10's side to the RS232C-levels on the PC's side.
Please note that the 3,5 mm jack plug and the earphone socket are stereo versions. One channel is used for audio and one for cloning data transfer.