What is the UA Flag on a Counter instruction?

[FactoryTalktotheHand]

Have a program I may have to translate from Logix 500 to 5000. The customer is using the "UA" flag on several counters. They're also using the "UN" flag just as often. The instruction help is, well, not all that helpful.

 

[bernie_carlton]

The 'UA' is specific to the High Speed Counter in the Fixed (and 5/01) SLC500 units. Bit 10 (UA) updates the accumulator word of the HSC to reflect the immediate state of the HSC when true.

The 'UN' indicates an 'Underflow', counting below zero - possible in a Down counter.

 

[daba]

....The 'UN' indicates an 'Underflow', counting below zero - possible in a Down counter.

correction - the UN bit indicates counting below the lowest number the counter can count to, not zero

 

[Mickey]

Here is what the book says...

 

[bernie_carlton]

Thanks for the correction.

 

[FactoryTalktotheHand]

Okay that makes sense. They were using it for on/off triggers in a ML1500 program. I think they are using an encoder on the high speed inputs of the 1500 (0-7) and those flags must update in real time independent of the scan?