TDK-Lambda Genesys series Technical Manual page 59

A structural register difference is, in all the RS-485 chained supplies, the Operational
Condition Event Register and the Questionable Condition Event Register are ORed together
to generate an event in the LAN supply's Questionable Condition Event Register bit 0. This
is called the ISUM bit and it may be used to set a bit in the Status Byte if an event occurs
in the LAN or any RS-485 supply
Other differences are:
− The Status Byte and Standard Event registers are global. These do not change as
different power supplies are selected with INST:SEL
− The Questionable Condition and Operational Condition registers are embedded in
the selected supply. These will change as different power supplies are selected with
INST:SEL
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