You don't need to send a string command to read a register. Only to write.
If you are actually writing to the controller, to a write-only register, send in the required data in msg.payload. Read the info tab in "Modbus Write" node:
For FC 5, msg.payload must be a value of 1 or 0 or true or false. For FC 15, msg.payload must be an array
[]of comma separated values true or false each. For FC 6, msg.payload must be a single value between 0:65535. For FC 16, msg.payload must be an array[]of comma separated values between 0:65535 each.
So, to set the motor to 100 percent speed, send "Modbus Write" node a msg.payload of 10000 (which would be 100.00% speed). This is very much the way yaskawa does it in their drives as well. I think the write node will also parse a string, but I would make it a good habit to use integers.
So, compare to the python code for setting the frequency on fan 1:
# set frequency # 10000 = 100%@50Hz
freq_1 = instrument_1.write_register(0x1000, 6000, functioncode =
6) # Register number, value, number of decimals for storage
print freq_1
So they're writing to register 0x1000 (which is register 1001 in HEX, 4096 in DEC) using function code 6 (preset single register) and setting it to 6000 (again, DEC) which is 60.00% speed. With the max speed being 50 Hz, 60% would be 30 Hz.
For fan 8, you would need another 'server' in the configuration with unit-ID set to 8. This would still communicate on the same RS485 as the other drives, but only fan 8 would respond.
