Falling Edge programmation on RSlogix 500

[guerino]

I everyone , I would like to know how can I programm a falling edge with RSlogix 500, the Rising edge already exist with OSR instruction but not the Falling edge. thank you

 

[Ken Moore]

 -]/[--------(osr)-----(bit)

 

 

[TConnolly]

If it does not matter if you get a one shot pulse on power up or when transitioning from program to run, then Ken's solution is by far the easiest. If however, you absolutely must have a true falling edge one shot then you might try something like the code snip below. Pay attention to the scan order when constructing a rung like this one.

The ML1200 and ML1500 actually have an OSF instructions, as do the PLC/5 and CLX.



(edit to add: Have you ever posted a snip and then discovered something that needed to be fixed? This is a snip from a program that's been running for years, and I just now noticed that the rung comment references an incorrect tag, AUTO_EVAC_BACKFILL instead of AUTO_EVAC. The comment is fixed now, but if the question had not been asked it might have stayed that way forever - not that it mattered though, this is the first time that file has been opened in probably five years.)

 

[mgvol]

You can use a one-shot falling (OSF) instruction if it is a MicroLogix 1200 or 1500.