CI-V stands for Computer Interface 5 and is ICOMs designation for their rig interface to a computer or to another rig. You can find it on most HF and some VHF rigs since the 1980s and is has not changed in it’s basic structure ever since. CI-V is a simple to use interface which allows, in contrast to other manufacturers designs, a “daisy chaining” of rigs, computers and other peripherals (see “Principle of operation”).

Historically, the Icom CI-V system started as a single wire connection at TTL (5V) level. This allows to very easily connect two radios or a radio and a peripheral (like an amplifier). Although this interface, a 3.5mm Mini Phone Plug (mono), is still available on most rigs, it has been augmented or replaced by serial, USB and wireless interfaces.

The old TTL level Remote interface requires a level converter to connect to a computer, usually to an RS-232 interface (see “CI-V interfaces”).

A few radios used to have both, the TTL level Remote connector and a RS-232 interface. Most Icom radios with a USB interface also have the Remote socket. The Icom IC-705 is the first modern rig which offers only USB as a physical connections, but additionally Bluetooth and Wifi are available for remote control and CAT functions.

The protocol (what and how information is transmitted) is quite distinct from other manufacturers designs, allowing for many options, but is sometimes more difficult to use and to debug (for the software author). This protocol has evolved over the past years, but always backwards compatible. More and more functions were added by using previously unused control codes. Older rigs support a basic set of functions, like setting and reading the frequency, mode etc. Newer rigs allow to remote control practically all functions the rig provides (see “Which rig supports which command?”).

Compatibility with the older Icom CI-IV system

The older version CI-IV is not compatible with CI-V. CI-IV was used at least in the venerable IC-751A and IC-R71. Icom used to offer a converter CI-IV to CI-V called UX-14, but this device is no longer available. Many years ago a US company named Piexx offered a replacement board.

What about other Icom rigs, handhelds etc?

The CI-V system is used by all Icom amateur HF rigs since the IC-735, all desktop receivers since the IC-R7100 and with some handheld scanners (IC-R10, IC-R20, IC-R30). Other Icom products like handheld two-way radios, marine products, FM mobile rigs don’t use the CI-V protocol and are not covered in this document.

I have looked briefly at the handheld Icom two-way radios, they seem to use a somewhat similiar protocol as CI-V, but incompatible. And usually these radios only allow ‘cloning’ with this protocol, i.e. copying memory contents and other settings from one rig to the other.