Bus Interface Unit Power Supply

The 24 VDC power supply in the Bus Interface Unit provides power for the Bus

Interface Unit itself and logic power for all I/O modules that may potentially be installed

at that station. External power must be supplied for field wiring of input and output

devices. Specifications for the BIU power supply are listed on page 1-11.

The BIU power supply is not damaged by either of the following:

Reversing input voltage on terminals 1 and 2.

Temporary overcurrent conditions on the 6.5 VDC output.

Timing

The Bus Interface Unit provides power to all I/O modules that are installed at the station.

I/O module operation is governed by a System Reset signal to ensure controlled

operation during the power up and shut down processes. As shown in the timing

diagram below, momentary power losses of less than 10 milliseconds do not affect I/O

module operation; however, longer power losses generate a Reset for all system I/O

modules.