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Modbus Protocol
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Author
Shashank Raut
Posted
14-Mar-2006 08:03 GMT
Toolset
C51
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 Modbus Protocol Shashank Raut
Hello,
I have implemented Modbus protocol as a client for multiple read (function code 0x04) and multiple write (Function code 0x10). I have used keil and IC P89C61X2
I have tested with Modbus simulator software and it works perfectly.
When I tried to interface with AB PLC, I observed that PLC is not able to get data from micro controller. PLC read response timeout was 1sec. I have observed signals (Tx,Rx) on CRO, when PLC send command for read, micro controller receives command and send information within 200msec. On PLC side timeout error comes. When PLC send multiple write command to micro controller, it gets data properly and send ACK but PLC is not able to detect ACK. This micro controller works fine with MODBUS simulator software.
Please help..
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Read-Only
Author
Shashank Raut
Posted
17-Jun-2006 03:19 GMT
Toolset
C51
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RE: Modbus Protocol Shashank Raut
I have not received any help from this forum but now I found the fault and this problem is solved.
The problem was with the parity bit sent by microcontroller, I have removed the bug with parity bit setting logic and it started working!!!!
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Author
Andy Neil
Posted
19-Jun-2006 17:08 GMT
Toolset
C51
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Dodgy simulator? Andy Neil
"I have tested with Modbus simulator software and it works perfectly."
So, it looks like the simulator is faulty, then?
I hope you have advised the supplier...
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Read-Only
Author
Shashank Raut
Posted
20-Jun-2006 02:42 GMT
Toolset
C51
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RE: Dodgy simulator? Shashank Raut
Yes, the simulator is faulty as it is not checking for parity bit in data reception.
I have informed simulator supplier about this.
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