CANopen Slave HTB Unit (Hybrid Terminal Block) Remote I/O connections with less-wiring for HMI expansion HTB means a CANopen slave unit containing 12 digital inputs, 6 relay outputs, and 2 transistor source outputs. One CANopen master unit is able to connect with up to 63 HTB units and one HTB unit is able to connect with up to 7 EX modules. That can configure a less-wiring remote I/O system