IEM3255 - Write to register (function code 16) issue

[shlomiAlk]

Hi,

I was trying to write CT value (address = 0x7ED, function code: 16 (10Hex)) by Modbus Poll but it doesn't work - I do success to read the registers (frequency, voltage for example without any problem).

The meter connected to my PC by RS485 to USB converter device.

I verified that the "Communication Protection" is disable and the multi traffic is on "By communication".

I used Modbus Poll after it doesn't work with my private gateway board, based linux OS, to make this problem to simple.

When I tried to configure other meter by Modbus writing command - no issue.

Do I need to add termination resistance?

do you have any other idea to solve it? things that I need to verify?

Thanks:)

[Ramasamy_N · Accepted solution]

Hello @shlomiAlk 

The Modbus register 2004 to 2036 are the meter setup and status registers and it does not allow to write directly using function code 16.

You can refer the user manual page 40 and above for the Modbus command interface. 

https://download.schneider-electric.com/files?p_enDocType=User+guide&p_File_Name=DOCA0005EN-13.pdf&p... 

The CT parameter can not write alone, we need to follow the command number 2000 (set wiring command - page 41) using the function code 16 to change the CT primary and secondary along with few other parameters.

Regards, 

Ramasamy N

[shlomiAlk]

Hi @Ramasamy_N ,

thanks for your reply.

I implemented code that send one block for all "Set Wiring" registers with one value changing of "CT Primary" to be 6002 (except CT Secondary, since isn't supported in IEM3255) and I got Meter result register ok (Cmd Reg result = 5376 return 0). When I read the "CT Primary" register, it doesn't changed (I verified by reading direct from Meter display).

I sniffed the bus and parse the data - please see the attached files.

I verified that the communication protected is enabled.

Do I need to do some action before I send Modbus set command?

I'm a little stuck with this issue and I would like for any assistance here.

BDY, I also send one block direct from ModbusPoll software to isolate the problem (maybe I have something wrong in my code) and it doesn't work.

many thanks.

[Ramasamy_N]

Hello @shlomiAlk 

The Communication protection must be disabled during the Modbus writing. 

Also the refer the attached screenshot of Wireshark traces when we write the set wiring command. 

The 24 parameters must filled properly and you can read the CT primary from the register 2030 (UINT16 format). 

Regards, 

Ramasamy N