Modbus communication

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Thread Starter

srinivas

dear sir, I am new to this protocol. I wanted to know how to communicate to an instrument supporting MODBUS protocol in RTU mode through Hyperterminal. Is it possible ? Please let me know the possibilities. I want to write a program in Visual Basic using the Mscomm control. Please let me have a bare idea atleast regards, [email protected]
 
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Not a problem, you can get everything you want to know about the protocol directly from Modicon. http://public.modicon.com/ in the support=>networks=>modbus area. Look for the Modbus Protocol Reference Guide. Regards, Alan Brause
 
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Christopher Eiden

If I were you I would go to www.win-tech.com and purchace their Modscan32 program. With the extra features it supports Automation thru VB and only will cost about $130. This cost is small compared to writing it from scratch. As with using hyperterminal alone you wont be able to talk Modbus.
 
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Srinivas Duddu

Eiden, First of all I thank u for the reply. I am interested in writing a code in VB using the MSComm control to read just two registers.Nothing more. I also had a modtest software utility of M/s Daniel Europe Ltd. With this i could communicate to the device using the following queries 010300000001840A and 010300060001640B.It works fine!! But i tried sending the same query using MSComm control in VB it doesnt work ! Please let me know where could be the problem!! Also suggest any links to VB code for MODBUS communication. Kindly suggest!! bye , Srinivas
 
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Srinivas Duddu

Alan, First of all I thank u for the reply. I downloaded the modbus reference guide from Modbus.org . It was informative but it doesnt mention any coding examples, I am mainly interested to write a code in VB using the MSComm control to read just two registers. I also had a modtest software utility of M/s Daniel Europe Ltd. With this i could communicate to the device using the following queries 010300000001840A and 010300060001640B. But i tried sending the same query using MSComm control in VB it doent work ! Please let me know where could be the problem!! Kindly suggest!! bye , srinivas
 
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mark kekkonen

communications with mscomm control to a modbus device have to be in binary, combined with a crc algorithm for both transmit and receive. You would be unable to use hyperterminal for this protocol. Mark
 
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