Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Manual de usuario descargar pdf (Pagina 307)

Special Programming Techniques

Chapter 19

192

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 OneShot

Input Pulse: Bit 112/04

Oneshot Bit: Bit 203/00

||

112

||

Application Program...

203

( SCT )

203

PR 002

AC 000

OFF

One Scan

railing 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 OneShot

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Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Manual de usuario Pagina 307