Addressing local data in a function block

I am trying to address a bit from the local memory of a function block, but am having difficulty. I am copying a global variable to a static variable within the FB, but then when I try to address the local bits directly I get incorrect information. As an example of what I'm trying to do:

Define 'local_in' as DWord in STAT area of block header (Address is 12.0)

Using ladder logic move global variable 'MD 1500' to 'local_in'

Use local bits L12.0, L12.1 etc in my program.

However if MD 1500 is equal to zero, I get none zero values for some of the local bits.

Any help would be most welcome, will save me an awful of a lot of time if I can make this function block work!!

Many thanks

Richard

Hello Richard,

I hope I could understand your problem correctly.

There's a difference between local data (TEMP) of an FB and STAT data.

The STAT (STATic) variablesare located in the instance data block which is assigned to the called FB and confusingly can be referred to as local data of FB in help files.

The TEMP (local data) is part of the CPU system memory that you can use for scratching (TEMPorarily)but not for storing data.

When you move MD1500 to STAT it means you move it to a double word register in the instance data block.

richardstarr

However if MD 1500 is equal to zero, I get none zero values for some of the local bits.

When you access L12.0 it means you are trying to access a bit in local memory (TEMP) which might not be clean and needs to be intialized.

You shouldaccess DIX12.0 instead of L12.0

If you still have a problem then I think it will be better if you upload your program here.

Best regards.

H-H