An optional input board that handles seven data (RS-422A). It only supports a 38.4-kb/s signal rate. As the RS-422 input and output boards are handled as a pair, the input/output size can be expanded in units of seven inputs and seven outputs. The maximum number of RS-422 ports for the IXS-6700 is 112, and that for the IXS-6600 is 56.