WinCC 2008 Alarm when DB address contains [text...] rather than numeric address

DanC2188

Member
Join Date
May 2013
Location
England
Posts
11
Just a quick query to all,

On site we use WinCC 2008 for HMI screens, some of the code has been written by other engineers and to determine the cause of some of the faults i take the alarm text, cross reference this in WinCC and look for the 'trigger address'. Most times i find a numeric address, for example - DB0.DBX0.0 but other times i find a 'trigger address' that looks like DB[text...] DBW0

I was wondering if there was a way somebody could explain to me why this is the case? as well as how to cross reference this easier between the HMI and PLC.

I hope this makes sense, i have attached a screenshot of this as well.


My apologies if this has already been asked on the forum but i do not have the ability to search prior to posting.

Thanks in advance.

Trigger Address Example.JPG
 
Just a quick query to all,

On site we use WinCC 2008 for HMI screens, some of the code has been written by other engineers and to determine the cause of some of the faults i take the alarm text, cross reference this in WinCC and look for the 'trigger address'. Most times i find a numeric address, for example - DB0.DBX0.0 but other times i find a 'trigger address' that looks like DB[text...] DBW0

I was wondering if there was a way somebody could explain to me why this is the case? as well as how to cross reference this easier between the HMI and PLC.

I hope this makes sense, i have attached a screenshot of this as well.


My apologies if this has already been asked on the forum but i do not have the ability to search prior to posting.

Thanks in advance.

This is called indirect addressing (or sometimes multiplexing). It means the tag doesn't point directly to one PLC address, but to several. Depending on what value is stored in DB_PLC_DB_SHIFT (the index), it accesses a different DB. If DB_PLC_DB_SHIFT = 1, then the tag accessed is DB1.DBW48. If the tag is 2, then it accessed DB2.DBW48.

This is often used when there is a common data structure used in multiple places. Instead of making 5 screens for the 5 identical cells in an assembly line, you can make one screen, and then have the tags point to whichever cell you want.

Methods like this make the HMI simpler/quicker to program or revise, and often have a lower file size/tagcount/screencount. The downside is that if it ISN'T working correctly, it can be a pain to troubleshoot. Essentially you have to troubleshoot it for one value, and then hope/assume the rest of the options work correctly, or troubleshoot the index tag instelf.
 
This is called indirect addressing (or sometimes multiplexing). It means the tag doesn't point directly to one PLC address, but to several. Depending on what value is stored in DB_PLC_DB_SHIFT (the index), it accesses a different DB. If DB_PLC_DB_SHIFT = 1, then the tag accessed is DB1.DBW48. If the tag is 2, then it accessed DB2.DBW48.

This is often used when there is a common data structure used in multiple places. Instead of making 5 screens for the 5 identical cells in an assembly line, you can make one screen, and then have the tags point to whichever cell you want.

Methods like this make the HMI simpler/quicker to program or revise, and often have a lower file size/tagcount/screencount. The downside is that if it ISN'T working correctly, it can be a pain to troubleshoot. Essentially you have to troubleshoot it for one value, and then hope/assume the rest of the options work correctly, or troubleshoot the index tag instelf.
Thank you mk42, i appreciate your reply your answer has helped a great deal.

Have a great day.
 

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