HP 44474A Digital I/O, used
The Agilent 44474A Digital I/O module provides 16 bi-directional data lines (bits) plus 4 lines used for control and handshaking. The 16 data lines offer TTL compatible input and open collector output. The 16 I/O lines or bits can be addressed individually (bit-by-bit), as two independent 8-bit ports, or as one 16-bit word. For instance, one port can be used for output operation, while the other for input. Each I/O line can sink current up to 0.125A from external devices.