Force in Simatic S7

The PLC is SIemens Series 414. I have a problem in forcing some vaiables.
In order to force the variable, I make a Vat,then entering the variable address and new/modifid value but the Force option is not active.for example I have a variable such as B3.DBW12 and I want to assaign a value to it.
It is noted that when I enter the address, it will bocome red coloured,indicating that the address is not correct.
I would greatly appreciate if someone can help me.

Regards,
Vahid

I don't think you can force datablock bits with an S7-300 or S7-400.

Sure you can. If the address is showing up as red, then it is a syntax problem. Are you absolutely sure you are typing it correctly?

For DB adresses, it is not called "force". Instead there is a column in the VAT where you enter the desired value. You then hit the button looking like a lightning arrow, and the value is transferred to the PLC adress. Beware that the value isnt kept forced, it can be modified by the PLC program.

If you have opened the special "Force" VAT, then I think you cannot enter a DB adress. But you can open another - normal - VAT, next to the Force VAT.

So you're saying for a DB address its "modify" instead of "force", and to "modify" a DB address in the ladder editor, you use the table that opens when you select Monitor/Modify instead of Display Force Values from the PLC menu?

In reply to S7Guy,first I supposed that Ihad written the address incorrect,but I checked the address and it is right,if you give me an email address I can send you the file indicating the address.
Thank you

No need, I beleive you.

The difference is in the two VATs that are being discussed. If you are using the Force VAT table, then you can't force DB values. Instead, just use the regular VAT table to force the bits. I assumed that was what you were using, which is why I asked if you had written it correctly.