The I/O Receiver module monitors three types of error
conditions: Daisy-chain power and continuity of I/O racks
downstream (CHAIN OK); parity of data output by CPU
(LOCAL PARITY); parity of CPU output data, driven by
an I/O Transmitter module, as detected by other I/O Receiver module(s) downstream (CHAIN PARITY).
Corresponding LED indicators, visible through the
module faceplate, turn off when the module detects
errors and function as troublshooting aids.