Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 63)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-16
Backup to Primary Data Transfer Command
The BACKUP TO PRIMARY DATA TRANSFER command lets you
enable the backup to primary data transfer function. When enabling or
disabling this feature, the processor must be in program mode.
When you enable BACKUP TO PRIMARY DATA TRANSFER, the
backup processor transmits up to sixteen words from the memory
communication module’s data table status section (beginning at S4:4) into
corresponding data table locations of the memory communication module
in the primary processor.
The following conditions must exist for the backup to primary data transfer
to occur:
Both the primary and backup memory communication modules must be
revision A/C or later.
The backup to primary data transfer function must be selected in both
the primary and backup processors via LIST function or message
command.
The number of words to be transferred must be created beginning with
S4:4. Note that there is no requirement to have the files the same length.
However, the backup processor will send only the number of words
contained in the smaller of the two backup and primary files.
This transfer occurs only in conjunction with a data table transfer or a
file transfer from the primary to the backup.