Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 74)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-27
You can check the status of each processor by looking at file 4, word 0 of
the status section. For further information about interpreting status words
refer to Using Data Table Status Bits in chapter 5.
Important: The PLC-3 backup system is not considered locked unless the
edit resource is acquired for both processors. When the PLC-3 backup
system is locked, a programming terminal cannot edit the ladder program
in the current context. Other programming devices must honor the edit
resource.
Unlock Command
The UNLOCK command lets you release the edit resource for both the
primary and backup processors; thus, allowing you to edit the program in
the current context with a programming terminal. The UNLOCK function
is equivalent to the UNLOCK SYSTEM function in LIST.
Enable Compare Command
The ENABLE COMPARE command lets you compare specific sections of
the ladder program in the backup processor with corresponding sections in
the primary processor on a word-by-word basis.
When the primary processor executes a message instruction containing the
ENABLE COMPARE command, the memory communication module
compares each section of the ladder program from the first rung through
the specified rung. If you set the limit for a particular section at zero, that
section will not be compared. If the memory communication module
cannot find the label comment number for a section, it will compare that
entire section of the ladder program. See Table 4.J.