Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 50)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-3
The following sections describe how to control memory communication
modules by using LIST functions and message instructions.
The LIST functions for memory communication modules follow the same
convention as other modules in a PLC-3 system.
Important: Concerning the operation of LIST functions, note the
following points:
If the primary processor faults, switchover occurs and the backup
processor takes control of outputs. The backup processor assumes that
LIST is active unless it encounters a program control command to
redirect control to the ladder program. When the primary processor is
repaired and restarted, it becomes the “backup” processor, and the
memory communication module resumes operation.
If the backup processor faults, all data transfers in progress stop until the
backup processor is repaired and restarted. Once the backup processor is
active again, the memory communication module resumes operation.
You can view the status of a memory communication module by making a
series of selections in the LIST menu. You can view the status of a memory
communication module from either the primary processor or the backup
processor Figure 4.1. If you make selections from the backup processor,
however, they have no effect on the operation of the memory
communication module until the backup processor takes control of outputs.
The only exception is the backup to primary data transfer function; it can
be accessed through the backup processor.
Important: In this manual, the term MCM refers to the memory
communication module not to the PLC-3 high-speed interface and
diagnostic software (cat. no. 1775-MCM).
Using LIST Functions
for Control