MODBUS RTU Slave Address Unknown


Thread Starter

pearl george


i'm a student doing my final project in data acquisition from trivector meter (ER300P - L&T make), at a substation near my college. In this i use the modbus rtu mode. here i have to connect 28 devices in a daisy chain connection. i can communicate with one device if i allocate a device address '01' but if i connect one more device to it, i get responses from both the devices randomly when polled continuously. i tried the modbus scanner too but it couldn't even get the connection.
is there a way i can find the 'device address'??
hi pearl george,

First allocate a different device address and then try to simulate with modscan..

Jimmi Shah

Fred Loveless

Sounds like you have duplicate addresses in the slave devices. All the devices that are in the same drop have to have a unique device ID. The RTU device address is a single byte so you can have a maximum of 254 addresses as 0 is a broadcast address.

Russ Bartels

You may want to check available documentation first. If these devices have never been accessed in this manner, there may be many that have the same address. In this case you will need to be able to change addresses in some of them.

pearl george

thank you so much for replying. i cud contact with l n t n obtained d register address (42385) at which the device id was present. so with function code 06, i wrote a unique device id for each device in the chain n cud get the connection completed for all the 28 trivector meters.

i also want to communicate with ER300P Energy Meter using Modbus RTU. Can u please suggest what hardware and software will be required?

It will be depend on what device or software you would like to connect with. basically for software, you need Modbus OPC software, there are many Modbus OPC offered in market. famous one is KEPServer or Matrikon.

For hardware, basically you will need RS-485 port. if you only have RS-232 or USB or ethernet, you need converter to RS-485 such as offered by Moxa.

Please give us more details so we can suggest correctly


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