correct structure for siemens DB

maico

Member
Join Date
Jun 2012
Location
Belfast
Posts
27
Hi All,
I am having an issue where I am communicating to an s7 414-2 plc via deltav I had 5 data set configured in deltav and all is working well I needed to add new analog outputs so added a new dataset, this is the 6th data set on the port of this card which should be ok as you can have 16 data sets per serial card.
My question is in my DB the last address that I can use is db101.dbx67.7 I have set up the data set to read the next address which should be db101.dbw68 which is an analog output but in the db after db67.7 I have an END STRUCT but on the next line I have no STRUCT before I start reading db101.dbw68 could this be an issue?

Thx
 
Hi,
the datablock itself can be seen as a struct. The length of the datablock can be found in the address column of the last END_STRUCT.
The block sizes are byte aligned, so if your last bool-variable address is at +67.7 then the size of the datablock is 68 bytes. Before the last END_STRUCT you should see =68.0 then.

If your application wants to read DBx.DBW68, this will fail. Due to optimized reading some s7-drivers are doing, maybe all other values from this DB can't be read then.

You can resize the DB by adding new variables to the DB and upload it into the plc. Right click on the last line, there is a context menu to add a line.

If you download the DB, then all variable values are set to the initial values. Keep this in mind, if you have setpoints for your process or other values inside the DB you want to keep.
 

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