Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 188)

Publication 1747-UM010B-EN-P - September 2003
B-8 M0-M1 Files and G Files
Specialty I/O Modules with Retentive Memory
Certain specialty I/O modules retain the status of M0-M1 data after
power is removed. See your specialty I/O module user’s manual. This
means that an OTE instruction having an M0 or M1 address remains
on if it is on when power is removed. A “hold-in” rung as shown
below will not function as it would if the OTE instruction were
non-retentive on power loss. If the rung is true at the time power is
removed, the OTE instruction latches instead of dropping out. When
power is again applied, the rung will be evaluated as true instead of
false.
You can achieve non-retentive operation by unlatching the retentive
output with the first pass bit at powerup:
M0:2.1
1
M0:2.1
1
B3
0
ATTENTION
!
When used with a speciality I/O module having
retentive outputs, this rung can cause unexpected
start-up on powerup.
M0:2.1
1
M0:2.1
1
B3
0
M0:2.1
1
U
S:1
15
This rung is true
for the first scan
after powerup to
unlatch M0:2.1/1.