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Modbus address range

Posted on 2007-11-28
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Last Modified: 2013-11-13
Hi, i am required to communicate with some modbus devices via tcp, i understand that i need to assign modbus addresses to these devices so i can get my data correctly. I read that the address range is from 400001 to 49999. i am just doing read only communications (i.e getting data from the devices) both analog and digital.

This is what i am doing now.

Generator running status - 400101
Engine speed - 400102
Common Fault - 400103

thanks
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Question by:jaxrpc
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11 Comments
 
LVL 27

Expert Comment

by:pseudocyber
ID: 20375737
I must confus, I had to look up what Modbus was.  

Have you seen this?  It looked like it might help you:

http://www.acromag.com/pdf/intro_modbusTCP_765a.pdf
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Expert Comment

by:pseudocyber
ID: 20375738
Confess, that is.
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Expert Comment

by:Darr247
ID: 20378428
Hmmmm... Registers 400101, 400102 and 400103 could each contain 1 eight-bit byte of data returned from devices (or all 3 registers could be getting input from one device, math functions, et cetera).
Is that what you're trying to do... peek at the register data in the controller using some kind of PC interface card in the controller's rack?
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Author Comment

by:jaxrpc
ID: 20520867
i think like what Darr247 said all these addresses are registers addresses. I used Modscan32 a free modbus software and i am able to peek at the data in these addresses. thanks
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by:Darr247
ID: 20522676
OK... sorry I couldn't tell you more, but I wasn't sure what you were trying to do from the question as stated. yvw.
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Author Comment

by:jaxrpc
ID: 20944121
Moderator : Please close this thread. Not interested in the answer anymore.
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by:Darr247
ID: 20944734
You are able to close it. If you feel our answers were of no help, then click the 'YES' button in your own reply (http://www.experts-exchange.com/Networking/Misc/Q_22989607.html?cid=238#a20520867) and follow the prompts.  Cheers.
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Author Comment

by:jaxrpc
ID: 21751629
no ans to my question
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Accepted Solution

by:
Darr247 earned 500 total points
ID: 21755719
> no ans to my question

Well, you didn't really ask a question.

You indicated you wanted to assign modbus addresses to some discrete devices, but that's not necessary.

Their inputs were already appearing in those 3 registers. They were technically assigned addresses as soon as they were wired to the programmable controller's input cards, and to access their data all you needed were those register addresses.
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