The Tektronix VX4801 provides 48 optically isolated TTL or CMOS compatible bidirectional digital I/O lines. The 48 programmable I/O signal lines are organized as six 8-bit bytes. Each of the six bytes can be independently configured under full program control. The sense of inputs, outputs, and handshake lines can be set to either active high or active low under program control. All I/O lines are both TTL and CMOS compatible, with up to 24mA of sink current provided for each output.