ModbusTCP data address fail

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Roger Miauton
Posts: 4
Joined: Mon May 26, 2014 12:26 pm

ModbusTCP data address fail

Post by Roger Miauton » Fri Sep 15, 2017 10:30 am

Hello,
i set up a Client and use the server "Modbus-Slave" for test.
I want to read out 2 holding registers with the adresses 40097 and 40098. This addresses are defined in the slave.
But the output TCP frame shows just 96 with two elements insted of 40096 with two elements.
It generates exeptioncode 2.
If i define the slave with the addresses 97,98 , it works.
What can i do, to read out the addresses 40097 and 40098 ?
See in pictures below.

thanks for your help.

PV780T, PVCS 2.8
Attachments
Modbus slave.PNG
Modbus slave.PNG (60.38 KiB) Viewed 70 times
PV Modbus1.PNG
PV Modbus1.PNG (84.8 KiB) Viewed 70 times
ModbusTCP frame.PNG
ModbusTCP frame.PNG (76.3 KiB) Viewed 70 times
boyce
Enovation Controls Development
Enovation Controls Development
Posts: 322
Joined: Wed Sep 08, 2010 5:09 pm

Re: ModbusTCP data address fail

Post by boyce » Wed Sep 20, 2017 2:15 pm

Looks like it is as expected. The leading 4 indicates it's a holding register. The data address is 2 bytes, does not include the leading 4.
modbustcp.JPG
modbustcp.JPG (74.29 KiB) Viewed 48 times
Boyce Schrack
Enovation Controls
Roger Miauton
Posts: 4
Joined: Mon May 26, 2014 12:26 pm

Re: ModbusTCP data address fail

Post by Roger Miauton » Wed Sep 20, 2017 3:36 pm

ok,
when this is the original modbus definition, then it seems that the Modbus protocol in the slave device in not correct implemented.
Unfortunately, i get an "illegal data address" response when i use the Murphy as client.
I will ask the producer of this device (photovoltaik inverter), and i hope they can adjust the address range of the slave.

Thanks for this information.
Johannes