Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 392)

Programming Technique
Chapter 25
25-2
When bit 112/04 makes a false-to-true transition, the one-shot bit (bit
253/00) is set on for one scan. The length of time bit 112/04 remains on
and does not affect the one-shot bit due to the next two rungs. Bit 011/14
is latched when bit 112/04 is set or bit 011/14 is unlatched when 112/04 is
reset. Bit 010/00 is then energized because the one-shot bit (bit 253/00) is
set for that scan.
During the next scan, either set of conditions prevents bit 253/00 from
being set. The one-shot bit is set for another scan only when bit 112/04
makes a true-to-false and then a false-to-true transition.
Trailing Edge One Shot
A trailing edge one-shot sets a bit for one scan when its input condition has
made a true-to-false transition. The true-to-false transition represents the
trailing edge of the input pulse. Programming for a trailing edge one-shot
is shown in Figure 25.2.
Figure 25.2
Trailing Edge One Shot
112
04
253
00
253
00
112
04
253
00
U
011
14
L
011
14
010
00
011
14
When bit 112/04 is set, bit 011/14 is latched. As soon as bit 112/04 makes
a true-to-false transition, the one-shot bit (bit 253/00) is set and bit 011/14
is unlatched. Bit 253/00 remains on for only one scan and energizes
bit 010/00.
The one-shot bit is set for another scan only when the input bit 112/04
makes a false-to-true transition then a true-to-false transition.