MicroMaster sending control words

I have looked at the forum, read the manuals, and searched on Siemens website, but I have not found the answer to this question.

When sending the control words STW and HSW do I have to send them as a one shot?

When I move 047F to the PIW 256 and 4000 to 258 or wherever the address is set, do I need to use a one shot move? If not, each time the OB runs it will be re-writing the same 047F and 400 to the Mircomaster. Is this going to cause any unwanted effects?

I do not have access to the actual hardware or else it would be easy to check.

Thanks for you patience and understanding with a newbie

Gabe

Hi, welcome to the forum!

The PIW is read continiously from the MM4 to PLC.
The PQW is written continiously from the PLC to the MM4.

So if you want to write to the command word, use the PQW.
===

When you are examining how the MM4 works, i find it easier to use adresses in the process image area (below 128 dependant of CPU type). Then you can use QW from "Monitor_modify", and also set individual Q-bits.

There's an example in the last post in this thread: http://www.plctalk.net/qanda/showthread.php?t=62823

Kalle