Fixed scan time in ML1200

[Mikey]

Is it possible to have a set scan time in AB Micrologix 1200.

If so how do you do it?

Regards

 

[kamenges]

To the best of my knowledge there is no specific way to run with fixed scan time on the ML series. There are ways you may be able to reasonably emulate this action, though.

Look at this thread for possible ideas. This thread ultimately addressed a different problem but it may give you some ideas.

http://www.plctalk.net/qanda/showthread.php?t=12206

Another thought might be to look at a delta of S:4 and use that to hold you off. You wouild need to use a JMP to stay in a loop at the end of your program. You would also need to handle rollover of the clock. But you could fix the scan time that way.

Keith

 

[TConnolly]

Use an STI subroutine for the functions that you need to have run on a periodic schedule. A Selectable Timed Interrupt is a subroutine that will execute at a selected rate, for example, once every 100 milliseonds. When the interrupt occurs, the main program is suspended, the STI routine (and any subroutines it calls) is executed. Then control return back to whatever the PLC was doing prior to the interrupt.

The STI routines are just a little bit different in the ML than in the SLC. Instead of setting up the STI under processor status, you set it up under function files.

Enter the number of the Subroutine at PFN. Set UIE to 1 (you can permanently set it or turn it on and off programatically). Enter the number of milliseconds between executions at SPM.

Refer to the ML documentation in the AB library for more information
http://literature.rockwellautomation.com/idc/groups/public/documents/webassets/browse_category.hcst