I am trying to interface Seeed Studio’s
RS485 shield for Raspberry Pi
along with the Python
Minimalmodbus
library on Raspberry Pi 2B -
NOT WORKING!!!
shield :
https://www.seeedstudio.com/RS-485-Shield-for-Raspberry-Pi.html
I tested following on Raspberry Pi:
It worked fine if I send data using Python
serial
library. It turns on a relay on a slave device and responds correctly.
ser.write(’\xff\x05\x00\x00\xff\x00\x99\xe4’)
It is not working if I use
Minimalmodbus
library for Python
instrument.write_bit(0,1,5)
minimalmodbus.NoResponseError: No communication with the instrument (no answer)
note: I used the same Minimalmodbus python code using another USB-to-RS485 converter on same RPi and it worked fine.
Python Code:
import minimalmodbus
import time
import serial
instrument = minimalmodbus.Instrument('/dev/ttyAMA0', 255)
instrument.serial.baudrate = 9600
instrument.serial.bytesize = 8
instrument.serial.stopbits = 1
instrument.serial.timeout = 1
instrument.mode = minimalmodbus.MODE_RTU
instrument.clear_buffers_before_each_transaction = True
instrument.debug = True
while 1:
instrument.write_bit(0,1,5)
time.sleep(5)
**error:** minimalmodbus.NoResponseError: No communication with the instrument (no answer)
Can anybody help if I can use this specific rs485-shield with Minimalmodbus library? Thank you in advance
Regards,
