Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 59)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-12
When you select the LOCK SYSTEM command, the memory
communication module attempts to acquire the edit resource for both the
primary and backup processors. The edit resource is defined as the ability
of a programming terminal to create and/or edit the ladder program in the
current context and manipulate the data table. If a ladder program is
already being edited with a programming terminal, the memory
communication module cannot acquire the edit resource until the editing
session is terminated.
Even though a PLC-3 backup system is locked, you can still:
create and delete PLC-3 memory sections
edit contexts other than the current context
Important: When the PLC-3 backup system is locked, a programming
terminal cannot edit the ladder program in the current context. Other
intelligent devices must honor the edit resource.
Important: The PLC-3 backup system is not considered locked unless the
edit resource is acquired for both processors.
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.
Unlock System Command
The UNLOCK SYSTEM 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.