Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 6 Oct 2008 15:38:14 -0500

On Monday 06 October 2008 09:18:39 David Dudley wrote:
> The calcout method sounds like what I'm going to use for this function.
> I was just wondering if there was another way (or a simpler one) to do
> the same thing.

There might be, especially if you want to have an EDM button pointing to the 
bo record to provide an ENUM interface to the value â with calcout that would 
need 3 records rather than 2.

> From my point of view, I want to only have the record process when the
> value changes, either from 0-1, or from 1-0.

The other mechanism built into the IOC that has "process on change" semantics 
is a CA link marked CP.  The bo record that actually connects to the PLC has 
OMSL="closed_loop" and its DOL field is a CP or CPP link to a "shadow" bo 
record in the same IOC which holds the new value to be output.  Only when the 
shadow record's value change does the CP link cause the output record to be 
processed.

The only tricky thing here might be at start-up, where you could need to use 
the SDIS & DISV fields of the final record to prevent the thing from 
processing when you reboot the IOC and the first value arrives.

HTH,

- Andrew
-- 
Talk is cheap. Show me the code. -- Linus Torvalds

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System