Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 307)

Special Programming Techniques
Chapter 19
19Ć2
When bit 112/04 makes a false-true transition, the scan counter begins to
increment once each scan. When the accumulated value of the scan counter
is equal to 001, bit 203/00 (the one-shot bit) will be on. The next scan, if
bit 112/04 is off, the scan counter will be reset to 000. If 112/04 is on, the
scan counter will increment to 002. In either case, bit 203/00 will be off
and remain off until 112/04 makes another false-true transition.
A trailing edge one-shot is used to set a bit on 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 19.2.
Figure 19.2
Trailing Edge OneĆShot
Input Pulse: Bit 112/04
OneĆshot Bit: Bit 203/00
|ą|
04
112
|ą|
00
Application Program...
203
( SCT )
203
PR 002
AC 000
ON
OFF
ON
OFF
One Scan
Trailing Edge
When bit 112/04 makes a true-false transition, the scan counter begins to
increment once each scan. When the accumulated value of the scan counter
is equal to 001, bit 203/00 (the one-shot bit) will be on. The next scan, if
bit 112/04 is on, the scan counter will be reset to 000. If 112/04 is off, the
scan counter will increment to 002. In either case, bit 203/00 will be off
and will remain off until 112/04 makes another true-false transition.
19.1.2
Trailing Edge OneĆShot