ET200M Analogue Inputs

MagicM

Member
Join Date
May 2015
Location
Manchester
Posts
3
I have just started commissioning an et200m link module over profibus, I have a number of analogue input cards that I can view using a vat table within the simatic manager software, the data for each channel is sent via 2 bytes, I want these two bytes to be in word format, does anyone have any hints to how I go about doing this?
 
Firstly, welcome to the forum.

I guess that you are quite new to Siemens programming and the addressing architecture. Everything in Step7 world is byte addressed but can be accessed as bits, bytes, words or doubles.

Each bytes contains 8 bits (0 to 7) an can be addressed as ByteX.ButY e.g. Input 4.7 (I 4.7)

Bytes can be address individually as in input byte 4 (IB 4)

Words are two bytes long so Word 4 contains bytes 4 and 5 and might be addressed as Input Word 4 (IW 4)

Double integers and Reals occupy 4 bytes so double 4 contains bytes 4 , 5, 6 and 7 and might be addressed as input double 4 ( ID 4).

There are better explanation on the forum if you do a search.

In your case, analogue inputs normally reside outside the process image and are usually addressed as peripheral words so your analogue input would be PIWxxx (Peripheral Input Word) where xxx is the number of the first byte.


You should also note that Siemens inputs are normally scaled to +- 27647

I hope this helps,

Nick
 
Thanks for your reply Nick, you are correct in thinking im new to siemens,
I understand your explanation of the various data types, I have managed to display an integer value of my analogue input whilst testing using a current simulator, the value indeed changes from 0-27000ish, which is a step forward from this morning, im still a bit confused to where I can access the address though, my two bytes of data are being received into a datablock named DB11 and are the 12th and 13th bytes.

Thanks again, Michael.
 
Hi MagicM(ike?)

If you want to have those two bytes, explicitly as a word, you could make a new DB, with a tag defined as word.

Then load the two bytes into that word:

L DB11.DBW12
T DBnew.DBWwhatever

Or, you could replace the two bytes in your original DB with one word. Make sure you don't mess up the layout :).

MagicM.jpg
 
Thanks guys, I've been able to address to the word now using DB11.DBW12 as suggested by boneless.

thanks again for the support. much appreciated.

Im sure I will be posting a few more questions soon.
 

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