yeah/neh on idea for SLC housekeeping idea?

[ganutenator]

Problem I am attempting to correct:
Make the SLC work more like the PLC 5 in the way in which oneshots work. In essence, make an ONS out of an OSR. To further expound... The SLC doesn't set their OSR's to one on prescan. The PLC 5 does. The benefit of this is the following:

// This is an SLC. The coil could pulse on first scan even though B3/0 didn't transition from false to true on its own (i.e. an actual discrete photo-eye input but no object went in front of it).

  B3/0   B10:0/0  B3/1

--|/|----[OSR]---( )

// This is a PLC 5. On prescan, the PLC writes a 1 to B10:0/0 to inhibit B3/1 from pulsing pre-maturely.

  B3/0   B10:0/0  B3/1

--|/|----[ONS]---( )

Idea:
If I reserve an array of words for oneshot useage. I could then set each word to a "-1" on first scan which would set each of the oneshot's memory registers to one. This would be very similar to the way in which the PLC 5 handles oneshots on prescan.

Good idea?
Bad idea?
You worry to much?
More useless time wasted?

 

[Allen Nelson]

You should have posted this as a poll

C. You worry too much.

How often is your PLC getting powered down? Most of my installs either operate 24/7, or

How often do you write a rung where the default conditions are usually false under normal conditions?

 

[Ron Beaufort]

looking for trouble?

Here's a link: just for hardcore One Shot worry-warts

PS - I think Allen's right - most people don't ever worry about this type of stuff and seem to get along just fine - still, if it's a critical application, your "set it to a one" idea sounds good to me -

 

[David Paik]

make sure that bit is used only once in your program.