Rockwell Automation 1775-MX_S4A,D17756.3.1 User Manual PLC-3 BACKUP CONC(OR.DU1 - Manual (Page 58)

Using the 1775ĆMX
Memory Communication Module
Chapter 4
4-11
Memory Download Command
The MEMORY DOWNLOAD command lets you transfer the entire
contents of the PLC-3 memory from the primary to the backup processor.
This transfer occurs once each time you request it, and has a higher priority
than the data transfer function.
The backup processor cannot take control of outputs if the primary
processor faults during the download. After the transfer is completed, the
LIST menu is redisplayed and the memory communication module
resumes operation.
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 and resume
operation.
- an error occurs during download. In this case, the memory
communication module aborts the memory download 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.
Lock System Command
The LOCK SYSTEM command lets you protect the ladder program in the
current context of both the primary and backup system from being edited
by a programming terminal. This protection remains in effect until you
unlock the processor or place it in program mode.
For this 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.