Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 79)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-32
Status On Command
The STATUS ON command lets you enable data transfer from the backup
processor to the primary processor.
When the primary processor executes a message instruction containing the
STATUS ON command, the backup processor transmits up to sixteen
words from the data table status section (beginning at S4:4) of the memory
communication module 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 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 be the same
length. However, the backup processor will send only the number of
words contained in the smaller of the two files.
This transfer occurs only in conjunction with a data table transfer or a
file transfer from the primary to the backup.
When enabling this feature, data table transfers and file transfers must be
stopped. An ERROR 12 will result if any transfers are occurring. Once the
STATUS ON command has been initiated, continuous data table and/or file
transfers may be re-enabled. If the command is sent to a memory
communication module of an earlier revision, an unknown command error
(ERROR 1) will result.
Status Off Command
The STATUS OFF command lets you disable data transfer from the backup
processor to the primary processor.
When the primary processor executes a message instruction containing the
STATUS OFF command, the memory communication module disables
data transfer from the backup processor to the primary processor. When
disabling this feature, data table transfers and file transfers must be
stopped. An ERROR 12 will result if any transfers are occurring. Once the
STATUS OFF command has been initiated, continuous data table and/or
file transfers may be re-enabled.