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#1 24-08-2007 15:23:34
- rakesh
- Member
- Registered: 24-08-2007
- Posts: 2
P8511 Modbus read issues
Hi,
I am using P8511 Ethernet temperature sensor and want to read temperature from the modbus register. I tried reading using a Sixnet VersTRAK uIPM RTU as well as from my workstation using Modbus Poll (mbpoll.exe) shareware. Doesnot work in either case. I am getting invalid address error.
I have configured address from 40001 and function i am using is 0x3 (block read) as per the P8511 documentation
Any idea on what could be the problem ?
Thanks,
Rakesh
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#2 27-08-2007 07:37:29
- PavelM
- visitor
- Registered: 29-05-2007
- Posts: 45
Re: P8511 Modbus read issues
Probably you have wrong settings in your modbus software. We tried read operation with Modbus Poll successfully. Below is image with setting.
You can use our SensorReader software for test. For capturing and debugging ethernet communication I recommend the Ethereal software.
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#3 30-08-2007 10:12:46
- rakesh
- Member
- Registered: 24-08-2007
- Posts: 2
Re: P8511 Modbus read issues
Thanks for the reply.
From the screen shot it looks like you have an older version of modbus poll software.
I used the same settings you mentioned with the latest version of mbpoll (4.3.1 Build 272 on WinXP).
The first read after a fresh connect is OK.
Probably because transaction id is zero.
000000-Tx:00 00 00 00 00 06 01 03 9C 40 00 0A
000001-Rx:00 00 00 00 00 17 01 03 14 00 E4 6F 6E 03 E8 FF CE 00 0A 00 1E 27 0F 6F 6E 04 E2 FD DA
The second read onwards mbpoll shows transaction id error. Compare first two bytes in the sequences above and below.
000002-Tx:00 01 00 00 00 06 01 03 9C 40 00 0A
000003-Rx:01 00 00 00 00 17 01 03 14 00 E4 6F 6E 03 E8 FF CE 00 0A 00 1E 27 0F 6F 6E 04 E2 FD DA
Looks like there is a bug in the latest version of mbpoll software or the latest version of mbpoll has exposed a bug in the sensor.
(say if the older verison of mbpoll always used transaction id zero...)
Anyways I can add code to send a modbus request and parse the reply.
Thanks again !.
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#4 03-09-2007 14:17:34
- PavelM
- visitor
- Registered: 29-05-2007
- Posts: 45
Re: P8511 Modbus read issues
You found a bug in our firmware. We fixed this in our new firmware 4-5-1.02. You can download this firmware from our www pages www.cometsystem.cz.
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