Perhaps this forum thread may help: https://support.industry.siemens.com/tf/ww/en/posts/read-digital-input/159925 

FrancescoBurgalassi

Hi all

I am trying to communicate between TIA portal V16 and LabVIEW. I created one DB in TIA portal and some variables in it. Now I would like to read these variables and write them from LabVIEW.

In TIA portal I deselected the "optimized memory access" option in the DB properties in order to obtain an offset for each variable in it.

Let's say that:

- my DB is DB_Name[DB5]

- The variable that I want to read is DB_Name.Variable_read (it is Real and its offset is 2.0)

- The variable that I want to write is DB_Name.Variable_write (it is Bool and its offset is 4.1)

In LabVIEW, I need to insert the "coordinates" of these variables in order to read/write them.

As regards the writing part (see following image), I need to specify (blue blocks):

- The DB number (which is 5 in my case)

- The Item offset in bits of the element inside the DB.

My first question is: how do I convert the offset 4.1 (that I read in TIA portal) in bits in order to give it as input to LabVIEW? I tried 34 (from 0.0 to 0.7 there are 8 bits, same from 1.0 to 1.7, 2.0 to 2.7, 3.0 to 3.7; in total 32. Then there are 4.0 (the 33rd bit) and 4.1 (the 34th bit)) but I got an error.

As regards the reading part (see following image), I need to specify (blue blocks):

- The DB number again (still 5)

- The number of items requested (since the command is Read real array, so must specify the number of elements in the array. In my case its just one)

- The item offset again, but this time in byte.

My question here is similar to the last one: I want to read a single real value and its offset in TIA portal is 2.0. How do I convert this into a byte that I can feed to the LabVIEW block? Also, is it right to specify "1" as the number of items if i just want to read a single Real variable?


Thank you for your help

 

Oh, Offset 4.1 means bit #1 of byte #4.

FrancescoBurgalassi

Thank you for your answer.

I already went through some of the posts you linked me, but all I could find were discussion specific to the link between LabVIEW and TIA portal.

My problem is more related to TIA portal itself I guess, in the sense that I need to understand how variables inside a DB are organized in bytes and bits and how I can calculate those numbers starting from variables' offests.

8 x 4 + 1

FrancescoBurgalassi

 I understand this, but I need to reference to the offset of the variable by just using bits. Hence how can i convert the offset 4.1 into just bits?

0_Einstein

Oh, Offset 4.1 means bit #1 of byte #4.

FrancescoBurgalassi

Thank you for your answer.

I already went through some of the posts you linked me, but all I could find were discussion specific to the link between LabVIEW and TIA portal.

My problem is more related to TIA portal itself I guess, in the sense that I need to understand how variables inside a DB are organized in bytes and bits and how I can calculate those numbers starting from variables' offests.

 

 

What "endian"ness is LabVIEW?  Use F1-Help in TIA Portal to see how bytes are stored for your specific PLC type (big or little endian).

You may need to adjust the bit value depending on the datatype actually stored.

For example, if the bytes are being retrieves as bytes, it should work as is.  However, if the LabView and the PLC are different "Endian", and LabView is requesting 16-bit data or 32-bit data and then looking at a specific bit within it, the byte order needs to be swapped first.

Or, you can store the data pre-swapped in the PLC DB LabView is reading.

Again, F1-Help "Endian" and in the instruction pane, search for "endian" to see available options.

FrancescoBurgalassi

 Tried that too, it doesnt work. Thank you anyway

0_Einstein

8 x 4 + 1

FrancescoBurgalassi

 I understand this, but I need to reference to the offset of the variable by just using bits. Hence how can i convert the offset 4.1 into just bits?

0_Einstein

Oh, Offset 4.1 means bit #1 of byte #4.

FrancescoBurgalassi

Thank you for your answer.

I already went through some of the posts you linked me, but all I could find were discussion specific to the link between LabVIEW and TIA portal.

My problem is more related to TIA portal itself I guess, in the sense that I need to understand how variables inside a DB are organized in bytes and bits and how I can calculate those numbers starting from variables' offests.