Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 97)

Programming Techniques
Chapter 5
5-16
1775ĆMX Module BackupĆtoĆPrimary Transfer Data Words
In response to the BACKUP TO PRIMARY DATA TRANSFER in LIST
or the STATUS ON command from a message instruction, up to 16 words
are sent from the backup system to the primary system. The backup
system transmits a maximum of 16 words from the MX data table status
area beginning at S4:4 into the corresponding data table status locations in
the primary system.
The number of words to be transferred must be created beginning with
S4:4. There is no requirement to have the files the same length. However,
the backup system will send only the number of words contained in the
smaller of the two backup and primary files.
You can use Data Highway or Data Highway Plus modules to connect the
primary and backup PLC-3 processors to a data highway. Two modules are
required, one in the primary processor and another one in the backup
processor.
Series A, Revision C (or earlier) 1775ĆKA Modules
When using series A, revision C (or earlier) communication adapter
modules, use the following guidelines:
assign a unique station address (000
8
to 376
8
) to each communication
adapter module
if the programs in the primary and backup processors are identical, then
you must:
- make sure all information sent to the primary processor is also sent to
the backup processor
- examine the run/backup bit on every rung used to transmit data
Programming Considerations
for Data Highway and
Data Highway Plus