smiffy

It is possible to get REAL (floating point) data over a modbus interface.
However, there is a caveat. The modbus protocol does not inherently understand REAL numbers - it only has the concept of BOOLEANS and 16-bit registers. REAL values are encoded in IEEE754 format, which are encoded into 32-bits. So each REAL value will have to be sent as 2 16-bit registers.
This is the duty of the application layer, as already stated, the modbus protocol has no knowledge of how to handle REAL values directly. So sending partner must ecode the REAL value into 2 16-bit registers and then send these. The receiving partner must then reconstitute these 2 16-bit registers back into a REAL value format. There are issues in doing this due to the way that different systems enocde the word order for REAL numbers (endian issues).
So the reason you are getting garbage could be down to:-
1) the word order of the data is mixed up
2) you have not converted the registers back into REAL numbers (e.g. took each register to be a REAL number which is nonsense as you would only be using have the REAL data).
3) The data really is garbage (wrong address or data is not REAL data).
This question has been asked before and is covered in these threads:-
/tf/WW/en/Posts/97287
/tf/WW/en/Posts/83233

This post was very useful. Thanks to Mr.Smiffy

In my current data report project we are not using PLC, Could you please tel me how to read the modbus floating value in Wincc RT Advanced using internal tags. My requirement is using EM6436 energy meter I need to show the values of modbus registers (43903 & 43913) on Wincc Runtime SCADA.

And I need to know how to swap the address as above you said [CD AB] format using internal tags.

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Split from Modbus RTU Help.

Hello JairaJ

if you want to change to swap the Bytes in the HMI Runtime then you have only the Chance to use VB Script.

for example this one:

https://foren.activevb.de/archiv/vb-classic/thread-382177/beitrag-382204/Re-Highbyte-Lowbyte-vertauschen/

(use Google Translator for non German)

or other Examples in the Internet for VB Script doing Binary operations.

Bye Murof

Hi Murof,

Thank you for your support. 

Actually WinCC RT Advaced support directly to Float IEEE754 data type format, so no need go to VB script.

I got Energy Meter (EM6436) values by assign Modbus Address like 403901 this is the right format, before i made mistake by assign address like 439001, this is the wrong format.

New question published by Mappy Manju is split to a separate thread with the subject Could share me the information how you made communication with energy meter & git the values right??.

Best regards
The Helping Hand