Download 1775-6.3.1, PLC-3 Programmable Controller Backup Systems, User

Chapter 4
Using the 1775MX
Memory Communication Module
Controlling the Operation
of Memory Communication
Modules
As shown in Table 4.A, you can control operation of memory
communication modules by using:
LIST functions (see page 4-3).
message (MSG) instructions (see page 4-16).
Typically, you use LIST functions during the development of your
application. This approach lets you select and deselect options manually.
In addition to providing additional selections, you can use message
instructions to automate memory communication module setup once you
are sure of the application. By inserting message instructions into the
ladder program, the memory communication module can be configured
automatically when powering up in the run mode or whenever the system
changes from program mode to run mode.
Table 4.A
LIST Functions and MSG Instructions
By Using:
You can:
4-2
LIST Function
MSG Instruction
transfer the contents of the data table from the
primary to the backup processor continuously
Yes
Yes
transfer the contents of selected files from the
primary to the backup processor continuously
Yes
Yes
transfer the contents of the data table from the
primary to the backup processor one time
No
Yes
transfer the contents of selected files from the
primary to the backup processor one time
No
Yes
stop further continuous transfers once the transfer
in progress completes
Yes
Yes
download memory from the primary to the backup
processor
Yes
Yes
control online editing capability for a
programmable terminal
Yes
Yes
compare the ladder program in the backup
processor with the one in the primary processor
continuously
Yes
Yes
transfer control to the backup processor
No
Yes
inhibit the backup processor from taking control of
outputs when the primary processor faults
No
Yes
transfer backup processor data to the primary
processor
Yes
Yes