Examining multi inputs if more than 1 needed

g.mccormick · Dec 23, 2015

What is the best way to examine multiple inputs at a time for setting an output.

For example lets assume that there is multiple dampers, each damper has an open position indicator. Before the vfd can be requested, N number of the dampers must be opened.
I have done an example in Do-more with 4 inputs and needing any 2 to be on for the output to be on. What about if I need any 2 of 8, or 3 of 16, etc. The ladder logic would get very big very fast. It seems that there should be a way to do this with bitmaps or something.

JeremyM · Dec 23, 2015

Are the inputs members of the same input card/file?

Look at that as a 16/32-bit integer (depending on the card) and think of a way to determine how many bits are '1'.

milldrone · Dec 23, 2015

g.mccormick said:
I have done an example in Do-more with 4 inputs and needing any 2 to be on for the output to be on. What about if I need any 2 of 8, or 3 of 16, etc. The ladder logic would get very big very fast. It seems that there should be a way to do this with bitmaps or something.

For 16 or less inputs You could use "casting", check the help file for details. Then use the "sumbits" function to get the number of bits that are on.

Use the import function under file to load this example into your simulator.

bernie_carlton · Dec 23, 2015

In any 'number of bits' issue I use a straightforward method which may be understood by anyone reading the logic.

Zero (clear) a numeric register.
The one rung for each bit, if true increment the register.
When done you have the nuber of ON bits. No cryptic logic. Just count the bits.

g.mccormick · Dec 23, 2015

bernie_carlton said:
In any 'number of bits' issue I use a straightforward method which may be understood by anyone reading the logic.

Zero (clear) a numeric register.
The one rung for each bit, if true increment the register.
When done you have the nuber of ON bits. No cryptic logic. Just count the bits.

Bernie that may be the best idea.

I was trying to imagine using bitmap of ints, XOR, or something else like that.

I'm actually going to do this in TwinCat, but same idea would apply.

I will create this in DO-more and post.

g.mccormick · Dec 23, 2015

Ok here is my example incrementing a count.

I am trying to get this in a "FOR" loop, using casting of the inptus X[ForIndex], but I'm having difficulty with the count just incrementing regardless of inputs.

Anyway here is an example.

g.mccormick · Dec 23, 2015

milldrone said:
For 16 or less inputs You could use "casting", check the help file for details. Then use the "sumbits" function to get the number of bits that are on.

Use the import function under file to load this example into your simulator.

Milldrone. That's great. Its easier than the increment way, the only drawback I see is that it is not as portable since different PLC's may not have the same casting and SUMBIT functionality. It is perfect for this discussion though.

Thanks

I also changed it so that X0-X7 cast to X0:UB to D0.

JeremyM · Dec 24, 2015

Computing the Hamming Weight should lend you portability.

osmanmom · Dec 24, 2015

maybe right maybe wrong

Doug-P · Dec 24, 2015

If you're up for it, there are several variations of 'counting bits set' you could adapt from C at http://graphics.stanford.edu/~seander/bithacks.html.

g.mccormick · Dec 25, 2015

JeremyM said:
Computing the Hamming Weight should lend you portability.

Thanks. I will have to see if I can figure out how.

g.mccormick · Dec 25, 2015

osmanmom said:
maybe right maybe wrong

I don't really quite understand what's happening in the math box. Can you explain?

osmanmom · Dec 25, 2015

have you simulate the program?

osmanmom · Dec 25, 2015

example,

Examining multi inputs if more than 1 needed

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