Remainder math register does not update when using DIV instruction

jendrus · Nov 28, 2011

Hello all, I am fairly new to Allen Bradley programming so bear with me.. ( I have prgogrammed microcontrollers and computers before). Im working on a ML1100.

I am trying to do a simple extraction of the last three digits from a four digit number (e.g. starting with a number like 3875, all I am interested in is '875'.) I figure I can do a DIV instruction ( Dividing the number by 1000 and moving the number in register S:13 to a location in memory. I have had no success doing this. The S:13 register always stays at 1. Attached is a picture of the code I have.

Any help is appreciated.
Thanks
Stan

jkerekes · Nov 28, 2011

N file types are integers. It will never show the fractional part. You need to use F file type which is floating point.

Earthscape · Nov 28, 2011

J, you beat me to it.

jendrus · Nov 28, 2011

Ok, so do i have to divide twice then? Im not sure how the remainder is formulated, whats with the fractional part? When i divide two floating point numbers (3875.0 by 1000.0 I expect to get 875 as the remainder, correct? I am not seing this.

jendrus · Nov 28, 2011

Exuse the dumb question but how do i get the decimal part alone in a memory location after the division. Im new with these data files in Allen Bradley pragramming. Thanks for the help

Peter Nachtwey · Nov 28, 2011

Is there a DDV instruction?

Earthscape · Nov 28, 2011

I think you can pull this off with a AIC and AEX instruction. AIC N20:99 ST9:0 , then next rung try AEX ST9:0 3 3 ST9:1 . You can then move ST9:1 back to an unused Integer if you want too.

Think that'll work.

bernie_carlton · Nov 28, 2011

Use the DIV instruction to divide one value by another value (Source A/Source B) and place the result in the Destination. If the Sources are single words and the Destination is directly addressed to S:13 (math register), then the quotient is stored in S:14 and the remainder is stored in S:13. If long words are used, then the results are rounded.

Note that S:13 must be directly used as the Destination to trigger the Quotient/Remainder behavior.

dcooper33 · Nov 28, 2011

jendrus said:
Exuse the dumb question but how do i get the decimal part alone in a memory location after the division. Im new with these data files in Allen Bradley pragramming. Thanks for the help

Perhaps this would work for you?

dcooper33 · Nov 28, 2011

Here's a screen-shot of the program in action...

OkiePC · Nov 28, 2011

bernie_carlton said:
Note that S:13 must be directly used as the Destination to trigger the Quotient/Remainder behavior.

I think Bernie has it nailed as far as how I read the original post. He doesn't need floats, just 32 bit math with 16 bit results. I also recall that there is a system bit that can affect the way overflow bits and remainders are used. I believe the default setting should give the normal result if S:13 is the destination.

dcooper33 · Nov 28, 2011

I tried using S:13 as the destination, and occasionally I get erratic results. You can see the discrepancy in the attached image. Is this because of a difference in the floating point and S:13/14 math, or is it possibly a quirk inherent in RSEmulate?

daba · Nov 28, 2011

I would just keep subtracting 1000 until the number was less than 1000.

Maximum number of jumps would be 32.

OkiePC · Nov 28, 2011

There is a way to do this, and a normal DIV should work. I, too, tried in on the Emulator, and I am pretty sure what I am seeing is NOT correctly emulated. I have a ML1000 I can fire up to try out after supper.

I think my previous comment about the system bit was wrong. I was thinking of the S:2/14 flag which affects the results of overflows.

Paul

jac · Nov 28, 2011

I'm with bmacattack33 that is exactly how I would approach getting the fractional only. I've wadded my way through a lot of good and bad programs and have never seen S:13/14 used.
Besides all math should be floating point!

Remainder math register does not update when using DIV instruction

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