I wanted to set up a communication between a Raspberry PI (slave) and my PC (Master) through Modbus protocol. Currently, I'm using modbus-tk (python) to set up the communication protocol.
The issue is that the Master was not able to read the register from the slave. May I know what is wrong with my code? I'm very confused.
The error that I obtained from Slave was:
Handle request failed: Invalid CRC in request or Request length is invalid
The error that I obtained from Master was:
ModbusInvalidResponseError
Note: the purpose is to use the Master to read the data from the slave.
Here is the code for the slave:
import modbus_tk
import modbus_tk.defines as cst
from modbus_tk import modbus_rtu
import serial
import time
modbusServ = modbus_rtu.RtuServer(serial.Serial('/dev/ttyUSB0'),baudrate= 19200,
bytesize=8, parity='N', stopbits=1, xonxoff=0)
print("start")
modbusServ.start()
slave_1 = modbus_tk.modbus.Slave(1)
slave_1.add_block ( "1", modbus_tk.defines.HOLDING_REGISTERS, 1, 5)
aa= (1,2,3,4,5) # data in the register
while True:
slave_1.set_values ("1", 1, aa)
time.sleep(0.5)
Here is the code for the Master:
import sys
import serial
#add logging capability
import logging
import modbus_tk.modbus
import modbus_tk.defines as cst
import modbus_tk.modbus_rtu as modbus_rtu
logger = modbus_tk.utils.create_logger("console")
while True:
master = modbus_rtu.RtuMaster(serial.Serial('COM3', baudrate= 19200, bytesize=8, parity='N', stopbits=1))
master.open
master.set_timeout(3)
master.set_verbose(True)
logger.info("connected")
logger.info(master.execute(1, cst.READ_HOLDING_REGISTERS, 1, 5))
Here is the datasheet and a picture of the USB-to-rs485 device that I am using to connect my Raspberry Pi and my PC:
https://www.enika.cz/data/files/produkty/komponenty/mereni-a-regulace/UT-890A%20User%20manual.pdf
https://c.76.my/Malaysia/ut-890-usb-to-rs485-converter-belco-1605-07-belco@2569.jpg
Thank you very very much for the help.
