Does INC_W in S7-200 one-shot itself or inc. every scan?

Hi all

I'm converting an S7-200 program into S7-300.

There is a Word Increment command INC_W which takes in a VW address and puts it back into the same VW address.

I want to replicate the logic in S7-300 so was going to just use an ADD_I and have it add '1' to the DB address.

However, I wondered if the INC_W increments the count every scan or does it one-shot itself so that if the power remains on it only increments once until the power goes off again?

Thanks for any light you can shed on this.

http://www.kjit.bme.hu/images/stories/targyak/plctechnika/qrc_e.pdf
http://www1.siemens.cz/ad/current/content/data_files/automatizacni_systemy/mikrosystemy/simatic_s7200/manual_s7_200_2005_en.pdf

As long as the condition is true it will perform the INC_W instructions.

Look for the conditions to see if it is a one shot |P| or triggered in a routine that is a one shot.

Regards,

Thanks for the info Garry.

There isn't one-shots on the instructions at the moment.

So am I right in thinking if the instruction is TRUE then every scan it will continue to add 1 to the address?

My memory was that it only happens once for each transition of EN, and that is born out by the manual that shows an Input being used to trigger the INC. But looking at my previous programs I always have a Rising or Falling edge before each INC. I have an S7-200 on the bench, so I will try it later. It is always the simple questions that make you go ????.

That would be great if you could try it for me Bryan. And you're right... it's always these simple things!

I don't have access to a 200 to try it. And when I do cut the wires to start the upgrade it could be quite serious if I get the functionality wrong as this value is controlling the speed of the machine. I don't want it suddenly screwing itself into the ground!!

Cheers

There was a good reason I had a Rising or Falling edge before each INC_W, if you don't it does count up every PLC cycle.

It is important to understand how it is used. With use by an interrupt you would not need a rising or falling edge.

Regards,

Bryan a big thanks for testing that for me. Very much appreciated.

Very good point Garry. I'll definitely bear that in mind.

Cheers