The ICP DAS I-7551 Photo-coupler provides a complete full-duplex (including control signal) electrical isolation channel between two RS-232 devices. This isolation is an important consideration if a system uses different power sources, has noisy signals, or must operate at different ground potentials.

The I-7551 provides the option of re-configuring which control signal is used i.e.  CTS can be selected instead of DSR, and RTS instead of DTR. The ICP DAS I-7551 incorporates two DC-to-DC converters, the isolation site of the I-7551 is located in the input and output interface circuit. In other words, the I-7551 is a 3-way isolation RS-232 to RS-232 repeater.