TRB145 does not connect to slave Modbus

I am trying to get values from my Modbus slave device connected to the DB9 connector on a TRB145. Unfortunately i get error messages like:

Request failed, result: Failed to get response: Operation timed out


Failed to send test request, daemon is down

I have setup the Modbus Serial Master like this:


In the slave device configuration i make a test request which generates the above mentioned errors.

How did I connect the TRB145 DB9 to the slave device?
Pin 1 (D-) to terminal A on slave
Pin 4 (D+) to terminal B on slave
Pin 3 (GND) to terminal C on slave

On the slave I activated a 120ohm resistor as this is the only modbus device.

I am looking to a solution to read my slave device.

Slave device configuration:
At first start, communication settings by default are: Baud rate: 38400 bauds;
parity: none; Stop bit: 1; Slave address :1

Ok, found it a schematic that I needed to loop pin 1,2 and 4,5 on the DB9 connector. Now I do get a response from the slave device:

Request failed, result: Failed to get response: Illegal data address

I got a table from the supplier like this,

Adress: 0x1200
Register number: 1
Format: 16bits unsigned
range: 0 to 24
Fundtion code: 0x03
The size of the status table is 18 bytes.


01 03 12 00 00 01 81 72

But using the FIRST REGISTER NUMBER 1200 in the request does give me the illegal address error.


Could you please try different Modbus Register Numbers to see if you get any data?

Devices from Teltonika Networks utilize Modbus Register Numbers, while certain third-party devices might prefer Modbus Register Addresses. The key distinction here is that numbers start from 1, whereas addresses initiate from 0. So, for instance, if a specific piece of data is stored at Modbus Register Address 101 on the Modbus Slave, you would need to access it from a your TRB145 device by referencing Modbus Register Number 102. So, to correctly correlate Register Numbers with Register Addresses, you would typically add +1 to the Modbus Register Address.

Kind Regards,

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