Schneider M221 memory word and value assignment

[JacksonP]

Hello,

I am programming a schneider modicon M221 in machine expert basic. I am trying to calculate a value and then assign it to another memory word.
-I name existing memory words in the tools-> memory word side panel
-I use the operation block to perform the calculation

%MW59 := %MW98*%MW99​

-I manually give %MW98 a value, %MW99 has a value from the HMI
-%MW59 remains 0, if I give it an online value it immediately reverts to 0.

The Yellow and black exclamation mark warnings are just saying I should protect my program. I tried several different %mw memory locations to move the value in. I also made sure when selecting a memory location to use that both used and equ used were unchecked before giving them a symbolic name and adding them into the programming.

I'm puzzled. but I'm sure it's something straight forward that I'm missing...I've been hunting through youtube for information but I can't find anything specific to this issue.

Thank you

 

[drbitboy]

50/1000 => (integer division) => 0, so %MW498 * (50/100) => %MW498 * (0) => 0

try (%MW498 * %MW99) / 1000, or ((%MW498 * %MW99 + (%MW498 / 2)) / 1000 if you want some rounding.

There might be a problem with integer overflow if %MW99 and/or %MW498 get too big; this may work better if performed with REAL (floating-point) values.

(%MW498 := 1000 / 499) then (%MW99 / %MW498) is mathematically correct, but then you will have problems with roundoff.

Welcome to the forum!

 

[JacksonP]

50/1000 => (integer division) => 0, so %MW498 * (50/100) => %MW498 * (0) => 0

try (%MW498 * %MW99) / 1000, or ((%MW498 * %MW99 + (%MW498 / 2)) / 1000 if you want some rounding.

There might be a problem with integer overflow if %MW99 and/or %MW498 get too big; this may work better if performed with REAL (floating-point) values.

(%MW498 := 1000 / 499) then (%MW99 / %MW498) is mathematically correct, but then you will have problems with roundoff.

Welcome to the forum!

.... what an embarrassing first post.... thank you, I agree this would work better with floating point numbers. I inherited this program and for whatever reason they have been using integers with just extra spaces instead of floating point with decimals. ie 100.0% from the HMI they would bring back as 1000 into an MW (int) instead of an MF (Float). and I have just been going along with it. I can't believe I didn't see that as a problem. I thought what is going on they are all integers! where is the clown emoji...

 

[drbitboy]

.... what an embarrassing first post....

Not at all! You posted enough detailed information that a fresh set of eyes saw the problem immediately.

Usually it takes a dozen or more posts before we get to the heart of an issue, so good for you for formulating a great question!

The likely reason you didn't see it and I did is that I have made this mistake many, many, many more times than you over the course of my career (hopefully less frequently as time went on ).