I pluged a waveshare usb->RS485 dongle and the port appeared is /dev/ttyACM0. I used the comand:
sudo mbpoll -a 255 -b 9600 -d 8 -s 1 -P none -t 3 -r 1 -c 2 /dev/ttyACM0
And I got:
mbpoll: modbus-rtu.c:110: _modbus_rtu_build_request_basis: Assertion `ctx->slave != -1' failed.
May you help me?