Quick RSLogix 5000 Question

[LemmingRebel]

Is there an "ON CHANGE" instruction? Say, an instruction that watches a value, and goes true when that value has changed?

 

[rubha]

1 line of logic will work for you

use a NEQ instruction
Value1 not equal to value2, set a bit, branch around bit with a MOV instruction: move value1 to value2.

 

[swhitlock]

No matter how you do it, you need to allocate one word of memory to store the value from the previous scan.

Assuming you're using the latest version of RSLogix 5k, I think you can actually write your own instruction that takes the watched value and a memory location as parameter.


Scott Whitlock
PLC Programming Articles:

http://contactandcoil.com/

 

[ChuckWoodbury]

A DTR Instruction works well. Data Transitional