2. CI-V level converter

To connect the CI-V bus line to a computer you need a converter, which converts the +/-12V of the RS-232 interface to 0V/+5V of the open collector bus line. ICOM offers such a device, called the CT-17. But there are several designs to build your own converter, the schematics are all fairly simple (and cheaper).

Here are some proposals for a converter: