Reading 2 registers with nb=1 when calling readRegisters function

[kunaala]

I'm reading through RTU mode as master at 38400 8N1 Master: Raspberrypi, connected to system running modpoll simulator in slave mode using FTDI cable

I'm able to read registers using the aforementioned function, But the modpoll simulator receives a request for reading two consecutive registers from the starting address.The value received from the simulator is in accordance with the same.

When I tried reading from the libmodbus (C) directly using modbus_read_registers, the response is as desired: reading 1 register at a time

Please help me in resolving this issue

[epsilonrt]

Could you :

• activate debug mode in your libmodbuspp test program and send me the information displayed ?
• send me the information displayed by the simulator ?
• send me your code ?

[kunaala]

In debug mode [01][03][00][F8][00][02][45][FA] Waiting for a confirmation... 01 03 04 00 00 40 40 CA 03

Simulator output Tx-> 01 03 04 00 00 40 40 CA 03 Rx-> 01 03 00 F8 00 02 45 FA

code excerpt: Modbus::Data<int, Modbus::EndianBigLittle> valread[2]; int regResponse = slave->readRegisters(addr, valread, 1); std::cout<<regResponse<<std::endl;

Please let me know if i need to attach something else

[epsilonrt]

Um ... I don't see the problem. an int is not coded on 32bits on your machine ? in modbus, a register is 16bits, so it is normal for the function to read 2 registers 16bits to make a register 32bits !

The syntax of the call to the readRegisters () function is bad, you should put: int regResponse = slave->readRegisters (addr, &valread[0], 1); even if it comes down to the same, it is better for what you want to do.

[kunaala]

Thanks @epsilonrt that worked! is there a way to make it machine agnostic for portability I would be keen on working on the same