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I/O Bus

The triplicated I/O bus transfers data between the I/O modules and the main processors at 375 kilobits per second. The triplicated I/O bus is carried along the bottom of the backplane. Each channel of the I/O bus runs between one of the three main processors and the corresponding channels on the I/O module.

The I/O bus can be extended between chassis using a set of three I/O bus cables. Communication Bus The communication (COMM) bus runs between the main processors and the communication modules at 2 megabits per second. Power for the chassis is distributed across two independent power rails down the center of the backplane. Every module in the chassis draws power from both power rails through dual power regulators. There are four sets of power regulators on each input and output module: one set for each of the channels A, B and C and one set for the status-indicating LED indicators.

Field Signals Each I/O module transfers signals to or from the field through its associated field termination assembly. Two positions in the chassis tie together as one logical slot. The first position holds the active I/O module and the second position holds the hot-spare I/O module.

Termination cables are connected to the top of the backplane. Each connection extends from the termination module to both active and hot-spare I/O modules. Therefore, both the active module and
the hot-spare module receive the same information from the field termination wiring.