The B868–001 register output module provides a 5 V TTL or CMOS-compatible interface between a PLC and peripheral field devices. The B868–001 register output module operates in either BCD or binary mode.

The desired mode is operator selectable, with the 16-bit output either having BCD values in the range 0000 to 9999 or binary output in the range 0000 (HEX) to FFFF (HEX).

The B868-001 is a 8-channel register output module with four 16-bit registers and is operated in channel select mode. In the channel select mode, only one channel (16-bit register width) is transferred during each cycle. This is accomplished by employing a simple form of handshaking with the PC. A channel select word is sent by the PC to the B868 module, directing it to send a specific channel to the addressed field device. The B868 then echos back to the controller the channel address of the last valid transmission. Channel select requires 1 input and 2 consecutive output registers. The input register contains the channel number echo, while the output registers contain the channel address and the data.