> > >Pardon me, but what is an "invert table?"
> >"Jiri's baby It allows for inverting the state of an input before it
> >gets to the logic engine. He's to lazy to hook it up to the right
> >contact on the field device"

Dave Pryor:
> Last month a large steel beam was dropped in my plant. Thankfully no one
> was injured, but it wiped out 6 N.O. prox switches. We only had five in
> stock. In our junk box there was 1 N.C. prox that would fit.
...

Thanks - I was beginning to worry I was the only one...

That said, though, I'm beginning to be a bit in two minds about inverts.

The problem is that if forces (& therefore inverts) are implemented in the core, nasty things are going to happen with inverts on points that aren't written every cycle.

OTOH, implementing forces in the IO drivers prevents forcing internal coils and other data table values, which is probably just as useful as forces on inputs, if not more so.

And, before you have the kittens about forcing internal coils, remember what the kitten said

Jiri
--
Jiri Baum <[email protected]>
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Jiri,

I'm not sure if I understand your last posting on the invert tables and how they would work. I never had any use for such a thing until I saw your first suggestion about having this feature. Then days later I remembered it when I had a problem that it would simply solve. Granted, I wouldn't use it as a permanent solution but it would have been a nice feature to have had.

Please correct me if I am seeing this differently than you are. An invert table would only be a mask that the I/O table would be checked against. Then only those bits would be inverted, but they would always follow the ACTUAL state of the I/O only inverted.

To my understanding a force table would be different. It would be a latched condition and each point could be latched ON or OFF and remain that way until that point is no longer forced.

Let me know if that is how you see it or am I confused.

Dave Pryor
[email protected]


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Both, I think.

You have it exactly right - that's how it would work.


However, from a mathematician's point of view, the two features are very similar, because there are exactly four things you can do to a boolean:
- nothing (0->0, 1->1)
- invert (0->1, 1->0)
- force on (0->1, 1->1)
- force off (0->0, 1->0)

I have a somewhat mathematical background, so I probably tend to see those four as more related than they appear to other people...


Jiri
--
Jiri Baum <[email protected]>
On the Internet, nobody knows if you are a @{[@{[open(0),<0>]}-1]}-line
perl script...

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