iFIX DI versus DO

Can anyone tell me what the benefit of using a digital input with the output enabled would be over using a straight digital output? We have several things here which I would consider digital outputs to a PLC, yet they are digital inputs which have the output enabled? Any thoughts?

Russ

A quick quess:

Read digital input from plc-1, write digital output to plc-2.

A quick and dirty way to pass bits between plcs, works well across different platforms, ie Allen-Bradley to siemens. Scada does all the work, don't have to buy special comm. cards etc...

Ken

Can anyone tell me what the benefit of using a digital input with the output enabled would be over using a straight digital output? We have several things here which I would consider digital outputs to a PLC, yet they are digital inputs which have the output enabled? Any thoughts?

Click to expand...

I have read this at least ten times, and I still don't know what you mean.

Where are the wires physically connected? In addition to what Ken mentioned, I have also seen cases where someone wired an output to an input on the same PLC to verify that the card wasn't bad (i.e., a blown triac output or something like that).

I wasnt aware that you could do that with a digital input (write to it). I keep all my discrete as DR (Digital Register). Sounds confusing though writing to a DI.

"I wasnt aware that you could do that with a digital input (write to it). I keep all my discrete as DR (Digital Register). Sounds confusing though writing to a DI."

Gotta be careful simply assigning everything as DR's. I used to think that was the easiest solution- however, some drivers (Bristol BR-3 comes to mind) don't like that approach and will choke up! Something to do with the way the different types of tags are handled in the scan.
Sorry- little off track but wanted to comment....
Mike

good idea

Ken,

Thanks, I guess I should have thought of that. I guess I can see the benefit now. It must be standard practice here to do that, even if there is only one PLC processor. Thank you.

S7, there are no wires, as Ken mentioned, all the data is transferred by the Scada.

Just a note to Steve and Arrow, we have absolutely no DR blocks here. I am relatively new to iFIX, but I have yet to see one here. The majority of what I have seen is either a DI, DO, AI or AO. Thanks for the input guys.

Russ