Problems with modbus RTU serial

English Forum
1

Hi,

I have a problem with connecting to device via usb - rs485 converter . I turn on bridge modbus/rtu serial and 1 meter then it shows error as below:

2025-09-08T14:16:46,463 [modbus0 ] ERROR [e.modbus.api.task.AbstractTask] Execute failed FC3ReadHoldingRegisters [meter0;unitid=1;priority=HIGH;ref=8192/0x2000;length=6] OpenemsException: Connection via [/dev/ttyUSB0] failed: Port [/dev/ttyUSB0] cannot be opened after [3] attempts - valid ports are: [ttyS4,ttyUSB0] 2025-09-08T14:16:47,071 [modbus0 ] ERROR [e.modbus.api.task.AbstractTask] Execute failed FC3ReadHoldingRegisters [meter0;unitid=1;priority=HIGH;ref=8202/0x200a;length=2] OpenemsException: Connection via [/dev/ttyUSB0] failed: Port [/dev/ttyUSB0] cannot be opened after [3] attempts - valid ports are: [ttyS4,ttyUSB0]

I use ubuntu and use minimalmodbus to test rs485 and it runs very stable, but when I put it into the program, the above problem occurs.

Thanks.

2

Hello, did you solve the prolem?? I meet it when i try to connect modbus RTU with openems. Thank you.