Micrologix 1500 scan

You may want to post your program so we can look at it

the scan starts with the first rung in you 'main' (2) then goes down from there stopping at each rung you have a JSR (another rung being called)..then returning to rung 2 (main) until it reaches then end of rung 2

that is the down and dirty...you can post you code then ask your question it will make it easier

Ok here it is. I hope I did this right

Typical Scan:


What is the bit your having trouble with. If it is being controlled by file 7 then it will not change state unless file 7 is run. It will remain in its last state until file 7 is run again.
I don't understand your timer questioned.
Why would you want to only run a subroutine when a certain screen is showing on your HMI. I personally don't like conditional subroutines, if I don't want something to operate I'll write that in the logic. But its your machine, I'm sure you have your reasons just curious.

I think you might be misunderstanding the program scan. It doesn't set there and wait for the next thing to happen -- it's all the time running the whole program, evaluating IO, etc. It scans the whole program (unless it not JSR'd) every time, every 10ms or so. If there's an alarm, it will process the appropriate code based on the conditions on the next scan -- at approx 100 times per second.

Study the page that Mickey shows above - it explains it very well.

boyd_man said:

but I need it to know as fast as possible when a fault accurse or the cancel push button has been pressed and react to it

Click to expand...

For fast... look at IIM, IOM and INT

answer Mickey's question and go into a little more detail of what you are trying accomplish

is your program running? are you just trying to modify it? starting/started from scratch?

boyd_man said:

I was under the impression that a file would not be scanned and no logic would work in that file if the subroutine was not active. I think I understand how the scan works if there is just one file but when there are multiple files I don’t understand how it scans them. Does it scan them all at the same time are does it scan them individually by the way you have placed you JSR . Can code be activated if the JSR for that file is conditioned out?

Click to expand...

1. When a subroutine is not scanned it is as if the file does not exist, all outputs in that file will remain in thier last state.
2. It will scan the subroutines individually ( one at a time) by the way you have placed the JSR's.
3. No, every thing in the file remains in its last state ( last time it was scanned)

Let me put this in Anglish for ya. It will run (on AB) top to bottom, left to right, kinda like you do when writing a letter.

That said, it starts ladder scan in File 2, since your first rung is a JSR it will go through that subroutine then come back to File 2, go thru the next subroutine until all are done then finish going through File 2 then update the data tables.

That thar means ifn ya got a 10ms scan time then any output changes will be made in 10ms or so BUT there may be things ya didnt think of.

An example may be an extended cylinder, the solenoid field may take a few milliseconds to collapse and allow it to retract. In many cases people do not move to the next step until the cylinder has been detected to be fully retracted; which may take more time.

So the scans may be fast but the machines cycling could take seconds, it just depends.

If a subroutine is conditioned then it will not be active until the condition is true.

If there are critical I/O in subroutines then look at using IIM or IOM instructions.

About the JSR thing, I have not completely looked at the code, but it appears that at least parts of the machine could still auto cycle. Ifn it was me and I was going to use JSR's all that would be in File 2 is the JSR's and divide the machine actions as necessary with faults/alarms being the last subroutine involved.

An added thought, have to be careful using the MCR instruction.

if a picture is sometimes worth a thousand words, then maybe this post will help ... notice the little "scan tester" ... experimenting with this in a "spare" program will often help you understand what IS and what is NOT being scanned ...

PS ... Phil changed the forum awhile back ... the [attachment] picture is still there ... it's just been relocated to the bottom of the post ...