Modicon 984 SUB Instruction

This video goes over the Modicon 984 SUB instruction.
This instruction is used for many operations beyond simply the subtraction math operation because the instruction is very low cost to the processor, and is therefore very fast to execute.
The SUB is often used as a "Copy" instruction, as well as to decide if a value is greater than, equal to, or less than another value.
This was a requested topic, if you want to ask about something Modicon or Allen Bradley related (500, 5000, Studio, View Studio, etc) put it in the comments section.

[@gabrielebattani2166]

Thank you so much

[@shortplcvideos5764]

I understand what you are saying. The controller should have detected the overflow and turned on the bottom right "Less than" pin, not treated the overflow like a normal result. Some of the Quantums are a little bit different than the 984's that I work on more commonly, I might have to go look at one and test what you're asking about and get back to you on it. Some Quantums have signed arithmetic, some instructions have 16 bit math that uses two registers. However, that should not cause what you are describing to happen!