Littelfuse CIO-120-MB Communications ModuleLittelfuse CIO 120 MB Communications Module Description The CIO MB CIO 120 MB communications module is a convenient and cost effective Modbus RTU interface capable of providing discrete control and monitoring of a 777 Plus Series overload relay power monitor over a Modbus network. The CIO MB is an I O module that provides four (4) digital inputs and two (2) AC DC rated relay outputs. The CIO 120 MB is an I O module that provides four (4) 120VAC inputs