Error 3441 in Proface Plc while compiling

i am Unable to set Output Variable to Input Operand inside the function block in proface. but i could do the same in Omron Plc. Y is it so??

I believe I have run into this exact problem in SCADAPack workbench function blocks.

You have a function block output variable and you want to use it within the function block as an internal input. SCADAPack Workbench is exactly the same - it will not me use an output variable as an internal input. The solution is to have two variables. One for internal use, and one for the output. You use the one internally for you internal inputs (where required), and the output variable is used once to set the output of the function block.

The way I do it, for example, with an analog input function block - I have a scaling function that outputs my EU (scaled value). I want this EU to be an output variable in the function block, but I also want it to be used internally for alarm determination. So I have two variables:

EUInt---REAL---Internal Variable
EU---REAL---Function Block Output

I set it up so that the scaled value coming out of my scaling function writes to EUInt, then the rung below that I move the value of EUInt into EU. For example:

-[SCL]---EUInt-----
-EUInt=EU------

Sorry, that's a terrible diagram. I hope that helps a bit. Unfortunately I cannot answer the question as to why it doesn't allow it, I know Studio 5000 and RSLogix 5000 allows it. Hoping someone else can answer that question too.

Thanks a lot bro. I too find the solution.. Instead of mapping the output variable as input operand, we can map that output one as local variable so that it can be used many times inside the Function Block.

Yea, that works too. I wonder if your Proface PLC is also unable to have timers within function blocks? If so, have you found a solution for that? In SCADAPack Workbench, a TON is a built in function block, but since I cannot use function blocks within function blocks, I cannot use the TON within my function blocks. It is rather unfortunate - maybe you have run into this same issue?

If you have, and you might have a solution, would you mind replying to my post here: http://www.plctalk.net/qanda/showthread.php?t=100758

Thank you!