The Mx4_EXP_128 (Mx4 I/O Expansion module for PLC applications) offers 128 user I/Os (64 inputs and 64 outputs) on a single card. Two Mx4 I/O expansion modules can be connected together to take full advantage of the Mx4’s full 256 I/O capability. The Mx4 I/O Expansion module includes two types of I/O interfacing connectors, opto-coupler compatible (Opto22, Gordos-compatible) and high-density TTL for customized interfacing.