RSLogix5000 CTU mnemonics

[judojames]

Can anyone tell me if the .OV mnemonic will reset a counter if the accumulator is greater than the preset value?

 

[mellis]

I think you are on the wrong track...

From the Instruction Help.
.OV
BOOL
The overflow bit indicates the counter exceeded the upper limit of 2,147,483,647. The counter then rolls over to -2,147,483,648 and begins counting up again.


This is a flag, not a control.

If you want to programmatically reset a counter, use the RES instruction.

If you want to reset the counter as soon as the accumulator is >= preset, then use the .DN to RES the counter.

 

[judojames]

Thanks for clarifying for me, I am using a reset sometimes counter counts above reset and does'nt reset to 0 with the .Dn bit being set. I installed a timer for redundancy. Why does the counters acc count higher than the preset value? It does'nt do it all the time.

 

[daba]

Thanks for clarifying for me, I am using a reset sometimes counter counts above reset and does'nt reset to 0 with the .Dn bit being set. I installed a timer for redundancy. Why does the counters acc count higher than the preset value? It does'nt do it all the time.

Yes it does do it all the time. If it doesn't, then you have additional code that is either resetting the counter, or preventing it counting anymore.

The .DN bit is simply a flag that the counter's .ACC value is "GEQ" (greater than or equal) to the .PRE value. The counter will continue to count regardless of any flags being set, .DN, .OV, or .UN

Also please note that even with the counter rung false, manually manipulating the .ACC or .PRE values with either the ladder window or the database monitor can affect the .DN flag. For instance if you manually put the .ACC GEQ the .PRE, then the .DN bit will come on. Counters belong to a set of instructions that do get "acted upon" when the rung is false, and the last thing the counter instruction does is test the .ACC against the .PRE to determine if the .DN bit should be on, or off.