WinCC Professional in TIA Portal: Cast PLC tags to different data type in HMI?

CDMAE1

Member
Join Date
Jan 2019
Location
North Carolina
Posts
2
Long story short, I am trying to map a DWord-type PLC tag as a Real-type HMI tag. I have a structure that stores arbitrary data, so depending on the application, the data block members can be interpreted as Reals, Ints, or Dints without having to create additional tags (good thing STL exists). But when creating an HMI tag, it automatically fixes the data type to the type in the PLC.

Is there any way to change this? I would hope that there is enough intelligence in WinCCP to simply interpret a bit string as a floating-point value, but then again, there have been a few things that have disappointed me in this software.
 
Hi CDMAE1, welcome to the forum.


First of all, is this an application for an HMI panel, or PC?



Not completely sure what you are trying to do, you only declare tags as DWORDS and use them as any other type where you need them? Why?



You can add a tag manually, just go to tag table, add tag and make sure it is defined for absolute access.

Tag.PNG
 
Boneless,

Thanks for the response. This will be for an HMI panel. The idea is that I have a function to detect a change in a tag value and log the old value. We need audit capabilities for the client but cannot use WinCC Audit for whatever reason (management, am I right?), so I need PLC code to handle that.

The purpose of using arbitrary data is so that I can have one big array of the UDT I created, and regardless of which value I pick to monitor, it can be used with a member of the array. The workaround, of course, is simply to create an alternative UDT specifically for REAL values, but I was just wondering if the more minimalist approach was possible.

I assume that absolute access can only be specified for DB's that have optimized access/symbolic access turned off in the PLC, correct?
 
Not sure actually, but worth a quick try :).


I hope it'll work!
 

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