What about interrupts and fast response modules?

[BobO]

As part of our new platform effort we are evaluating things like interrupt routines that could be triggered by hardware timers, inputs, and presets associated with hardware counters. It is very straightforward how to do this on the new hardware, but we also see how it might be done on DL205 and Terminator. Which then begs the question: 'Should we?'

So...thoughts please? Do you use interrupts on existing controllers? If so, how fast a response time on inputs and outputs is required? What kinds of applications do you do?

[Controls Guy]

I haven't done it a lot, but when I have done so, it's been divided about equally between two applications:

(1) what you'd normally picture using interrupts to do, catching a fleeting input or reacting to one at faster-than-scan speeds, and

(2) high-ish speed counting, like in the sub-kHz but faster than scan range (using either interrupt I/O or generic but fast discrete inputs read on an interrupt timer), when I was too cheap to buy an HSC module.

[BobO]

OK...I confess, I expected more response to this. I guess I am learning a very valuable lesson about PLCs, and that is that most folks just do basic scan bound stuff, and despite our tendency to focus on 'gee whiz' features, most aren't required.

Until they are...

[ATU]

For cyclical machines, interrupts are quite handy. Especially if you could tie them into the high speed counter to create a PLS in the controller. An interrupt task would be perfect for that.

[BobO]

Current thought is to have 4 channels of high speed counting with preset tables that could fire interrupts, as well as set, reset, and toggle outputs directly, and to reset the counter. All of that would be hardware based...very fast. I would also have inputs be capable of firing interrupts directly, as well as microsecond timers for precision intervals. Hopefully, taken together, that would provide a pretty good bang for not much hardware cost.

[ATU]

Will you be able to access and change the preset tables on the fly?

[BobO]

Will you be able to access and change the preset tables on the fly?

Yes. It would all be instruction based. The system config would only be used to define the basic I/O setup...what inputs assigned to what functions, etc.

[ATU]

Adjustable filters on the HS counters?  That worked well on the 205 modules.

[BobO]

Adjustable filters on the HS counters?  That worked well on the 205 modules.

Yep.