Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 73)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-26
Important: A memory download will not occur if:
- the backup processor has insufficient memory to accommodate the
memory contents of the primary processor. Should this occur, the memory
communication module will abort the memory download function and
resume operation.
- an error occurs during download. In this case, the memory
communication module aborts the memory download function and the
backup processor shuts down.
-the keyswitch on the primary processor is in the MEMORY PROTECT
ON position. This causes the primary processor to display an error message
unless the ignore keyswitch option is enabled on privilege 72.
Important: If you are using a series A, revision C (or earlier)
communication adapter module (1775-KA) in the backup processor, you
must change its Data Highway station number after performing a memory
download during initial system configuration.
Lock Command
The LOCK command lets you protect the ladder program in the current
context from being edited by a programming terminal. This protection
remains in effect until you unlock the processor or place it in program
mode. The LOCK function is equivalent to the LOCK SYSTEM function
in LIST.
When the primary processor executes a message instruction containing the
LOCK 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 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.
For the LOCK command to function properly, the primary processor must
be in run mode or test mode. If you switch the primary processor to
program mode, the memory communication module unlocks both the
primary and backup processors.
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