Modicon Logic Question

[gitargr8]

I'm doing a Modicon to ControlLogix conversion, and I'm seeing a few rungs like the one in the attached image. Firstly, according to the manual, the top timer output turns on when timer = preset and the bottom turns on when timer < preset. Do one or both of the inputs need to be on for the outputs to turn on? Secondly, why the heck would someone add 1 to a value, then clear it in the next instruction? It also looks like they're doing the same with the timer accumulator. Any help is much appreciated. Thanks, ~Ryan

[Crossbow]

SUB is sometimes used as a compare, as the 3 outputs are greater, equal, and less than. Check the 984 Ladder Logic Block Library manual, which I think is in the Downloads section here.

[gitargr8]

Yeah, I figured that part out, but isn't the timer's accumulator here being overwritten with 0 all the time?

[gitargr8]

Actually now that I've gone through a bunch of the code I'm thinking that the SUB is just attached to the top timer output, not both the top and bottom. So basically the timer gets reset when it goes done. This editor really makes it tough to see where the shorts are, and where the inputs / outputs off the instructions are. Is there any setting in ProWorx to change this?

[Crossbow]

Nope, that's how it's going to draw it.. If you want space, you have to add one manually like in column 4. I hated working with that software. That PLC has so few commands available it's a pain to write anything. Then there's the fact that Modicon logic processes down and then across, not like normal PLCs or the way we read a book.