Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 44)

Installation
Chapter 2
2Ć32
Figure 2.13
Example of a Rung that Sends a Message during switchover from primary PLC-3 to backup
PLC-3.
EN
MSG
MESSAGE TYPE
CTL = FB200:00001 = 0
CHANNEL: E2.5.
#H045$N4:17= $B3:5
DN
ER
00
E0000
00
01
S0003
17
1
STAT
12
STAT
15
STAT
13
E0000 E0000
E0000
00
01
E0000
L
17 01
E0000
U
S0003
NOTE: Bits E0000/00 and E0000/01 are internal storage bits. You can use any unused data
table section to reference these bits. Bit S0003/17 is the run/backup bit.
Using Automatic Switchover
After you select the BACKUP OPERATION for a rev. D. (or later)
1775–KA module, you may want to use automatic switchover for your
PLC–3 backup system. During automatic switchover:
the 1775–KA module for the primary PLC–3 processor disables its
Data Highway port.
the 1775–KA module for the backup PLC–3 processor becomes the
address that you selected with the LIST function (rather than the
corresponding address it received during the BACKUP OPERATION).
NOTE: You cannot select the BACKUP OPERATION for a multidrop
modem applications because the modem port will not become disabled
after a PLC–3 processor fault regardless of the switch settings on the
module.