CompactLogix - 1769HSC - Ring Counter

[bernie_carlton]

I've done all of one whole project using the CompactLogix and the 1769-HSC and that was using a linear counter.

Now I'm trying to use a ring counter. The count cycles the way it should (up to 'max' then restarting at 'min') but the 'overflow' flag doesn't clear (at least the way I think it should) when the progrom turns on the 'overflow reset' bit. Is there any trick to this? Is there any kind of timing diagram showing the relationship of these signals? Should the 'reset' stay on while the 'overflow' bit is still on? I basically have right now:

      ring

--| overflow |---+----[ONS]---------( stuff )---

                 |

                 |               ring counter

                 +-------------( overflow reset)-

Should this work?

 

[10baseT]

Try one shotting the reset , I would have though that a transition was necessary to get a result ,otherwise , you could just leave it on - this of course may be complete twaddle , but give it a try .

 

[bernie_carlton]

I tried that - it got worse. I'll be back at it Monday morning. I may have to roll my own detection of the overflow if I can't get it to work this way. The manual gives just a few sentences concerning this operation and absolutely no timing diagrams. The counter in a Micrologix 1200 was much more friendly.

Also RSLogix5000 massages the registers from the counter in such a way that I can't correlate error codes to the tables in the manual. Ah well, I guess it must be progress.

 

[rdrast]

Is that counter module on asynchronous scan as in Logix I/O? If so, you need to set the reset bit, and unlatch it when you get a status bit of 'Reset Read' from the counter module.

 

[bernie_carlton]

Looking for a 'reset read' would be fine if one existed. But it doesn't. Conditioning by using the actual overflow bit is basically the same thing.

I corrected a few things regarding my method of runtime configuration of the module and the correct input voltage. It seems to be behaving a bit better now. I didn't one shot the reset but furhter conditioned it with one of the bits from the current count. That way if it doesn't reset immediately I strobe it again. As long as the overflow bit goes off before the next cycle its ok.