Modbus-RTU: Only first byte of answer is read from my device about modbus

[nqv]

I should provide expected length to read from serial port for each command.
What if you put time.Sleep(300 * time.Millisecond) before syscall.Select (serial_linux.go:123), will you have full response data?

[gonium]

@nqv: Thank you very much. If I insert a sleep time, I can correctly receive the data (and the data is also correctly decoded, see my last commit). I guess that you can determine the sleep time from the baudrate and the expected response length.

[nqv]

@gonium Thanks. I'll fix this issue as you have suggested.

[nqv]

@gonium Thanks for your pull request, I believe the issue has been fixed. I'd be grateful if you can test and let me know if it works with your device.

You also need to run go get -u github.com/goburrow/modbus to also download github.com/goburrow/serial as I move the serial part to another repository.

Thanks

[gonium]

@nqv I just switched from my temporary fork back to your master - now everything works as expected. Please note that I am currently using the SDM630 device in its factory settings: 9600 8N1. I didn't test higher baud rates.

Thank you very much for your help! Closing this for now.

[arnavbansal95]

@gonium How to connect Pi to TTL to 485 Converter?

[gonium]

Hi @arnavbansal95, I prefer using cheap (as in 3 USD) USB-to-RS485 converters. If you really need to connect directly to the extension header of your RPi you can have a look at the schematics of this Sparkfun RS485 shield.

[arnavbansal95]

@gonium Thanks ....I also got a Usb to 485 converter....but I don't know how to install its driver on raspian as I am new to linux....could you help me with that?

[NilanjPatel]

@gonium how you did sleep thing to to read energy meter??

[surbhigup]

@gonium i am also working on it but didn't get the result. Can you give me some help that how you send query?