Abstract: In a data processing system which includes a base central processing unit, channel, and input/output (I/O) interface to which peripheral devices may be attached, a special attachment is disclosed. The attachment made to the base I/O interface includes connector circuitry which is required when the signals on the input/output interface must be repowered to peripheral devices in an expansion input/output unit, power isolation must be provided between a base data processing system and I/O expansion unit, or a remote peripheral device is to be attached to the base data processing system I/O interface. The connector circuit includes logic which responds to the normal I/O interface signals to energize drivers in the connector circuit to achieve repowering of signals on bidirectional signal lines and unidirectional signal lines.