Modbus RTU with Knot

RouterOS General
1

Hello,

I’m new to Modbus RTU and want to get values of a SDM230-Modbus Single-Phase DIN rail Meter.
(https://stromzähler.eu/media/05/ae/19/1696582672/sdm230-modbus.pdf)

The ID of the energy-meter is set to 111.
Baud rate is set to 9600 on the Knot and energy-meter. Wired connection is correct, too.
Function should be Read Input Register (FC 4), I think.
I tested several commands like the following to get the value Active power in watts (register 30013):

iot/modbus/transceive address=111 function=3 values=30013
iot/modbus/transceive address=111 function=4 values=30013

But all the testing leads to “failure: Timeout”.

Can someone please help me or give me a hint to get the right command?

Kind Regards

2

It is the 30013 that is not correct, it is the address of the register, but not the Modbus address.

Seemingly there is a base address of 30001 (which corresponds to Modbus 0).

30013 becomes 000C (see page 15 of the pdf you posted a link to).

as a matter of fact 30013-30001=12 → 0x000C

The syntax should be something like:

/iot modbus transceive address=111 function=4 data=000C0002

(for some reasons that device seems to need an even number, so 1 register=02, 2 registers=04, etc.)

data is the actual hex string
values is a comma separated array of decimal values, check:
https://help.mikrotik.com/docs/pages/viewpage.action?pageId=61046813
using values, it would probably be:

/iot modbus transceive address=111 function=4 values=0,12,0,2

See also this thread:
http://forum.mikrotik.com/t/knot-modbus-rtu-write-registers/177356/1

3

great, thank you :slight_smile:
now it`s clear to me