[Document sharing]-Modbus Dev

QuecPython
1

Basic illustration

This article tells how to used modbus DTU.

Application case of modbus

from usr.sensor import ModbusInit
import usr.uModBusConst as Const
from machine import UART
import utime as time

# LightSensor UART info
uart_port = UART.UART0
bardrate = 9600
databits = 8
parity = 0
stopbit = 1
flowctl = 0
# sensor addrinfo
slave = 0x01
const = Const.READ_HOLDING_REGISTERS
start_addr = 0X03
coil_qyt = 0x02
# light data transfer
def light_data_transfer(ret_str):
    str_list = list(map(lambda x: x.decode("utf-8"), ret_str.split(b",")))
    data_bits = int(str_list[2])
    data_list = str_list[3: 3+data_bits]
    one_place = int("0x" + data_list[0] + data_list[1], 16)
    tens_place = int("0x" + data_list[2] + data_list[3], 16)
    return tens_place * 10 + one_place

if __name__ == '__main__':
    modbus = ModbusInit(uart_port, bardrate, databits, parity, stopbit, flowctl)
    while True:
        modbus.write_coils(slave, const, start_addr, coil_qyt)
        ret_str = modbus.read_uart()
        print(ret_str)
        digit_val = light_data_transfer(ret_str)
        print(digit_val)
        time.sleep_ms(1000)

Application note of modbus API

modbus_utils.init (uartN, buadrate, databits, parity, stopbit, flowctl)

Initialize UART port

Parameter Type Illustration
uartN int UART0 - DEBUG PORT UART1 – BT PORT UART2 – MAIN PORT UART3 – USB CDC PORT
buadrate int Baud rate, common baud rates are supported. 4800、9600、19200、38400、57600、115200、230400
databits int Data bits (5~8), the Unisoc just supports 8 bits
parity int Parity validation（0 – NONE，1 – EVEN，2 - ODD）
stopbits int Stop bits（1~2）
flowctl int HW flow control（0 – FC_NONE， 1 – FC_HW）

modbus_utils.divmod_low_high(addr)

Split the high and low bit of address

Input parameter Type Illustration
addr int Hex address
Returned value Type Illustration
high int Hex address of high bits
low int Hex address of low bits

modbus_utils.calc_crc(string_byte)

Calculate the value of bytearray parity bit.

Parameter Type Illustration
string_byte bytearray bytearray
Type of returned value Type Illustration
crc_high int CRC high bit address
crc_low int CRC low bit address

modbus_utils.split_return_bytes(ret_bytes)

Split the bytes read from UART port and convert as bytearray

Parameter Type Illustration
ret_bytes bytes bytes
Type of returned value Type Illustration
bytes_split list List after splitting bytes, the format is shown as [b’00’, b’1E’, ……]

modbus_utils.read_uart()

Read the uart data and return bytes value

Type of returned value Type Illustration
bytes_string bytes Format ： b”01,1E,1F……”

modbus_utils.write_coils(slave, const, start, coil_qty, crc_flag=True)

Write coils

Parameter Type Illustration
slave int Device address
const int Functional code
start int Starting address
coil_qty int Read coil quantity
crc_flag bool Whether the parity is needed
Type of returned value Type Illustration
status bool Return True

modbus_utils.write_coils_any(*args, crc_flag=True)

Write any coil address

Parameter Type Illustration
*args list List by any byte
crc_flag bool Whether the parity is needed

Functional code list of uModBusConst

Name Address
READ_DISCRETE_INPUTS 0X02
READ_COILS 0X01
WRITE_SINGLE_COIL 0X05
WRITE_MULTIPLE_COILS 0X0F
READ_INPUT_REGISTER 0X04
READ_HOLDING_REGISTERS 0X03
WRITE_SINGLE_REGISTER 0X06
WRITE_MULTIPLE_REGISTERS 0X10
READ_WRITE_MULTIPLE_REGISTERS 0X17
MASK_WRITE_REGISTER 0X16
READ_FIFO_QUEUE 0X18
READ_FILE_RECORD 0X14
WRITE_FILE_RECORD 0X15
READ_EXCEPTION_STATUS 0X07
DIAGNOSTICS 0X08
GET_COM_EVENT_COUNTER 0X0B
GET_COM_EVENT_LOG 0X0C
REPORT_SERVER_ID 0X11
READ_DEVICE_IDENTIFICATION 0X2B
1 Like
2

I want to implement modbus using QuecPython on the EC200U-CN. But I’m getting an error that the modules usr.sensor and usr.uModBusConst don’t exist

3

hi, Tanmayee

Please refer to the following script.

modbus_RTU.py (22.1 KB)

5

hi，Sumeri

Thank you for your information. I am confirming it. I will give you feedback as soon as possible

6

Hi Felix,

There was the problem with Logic Level Convertor at the end of MAX485. I have changed logic level convertor. Now, Its working fine. That was a hardware issue. I am sorry for rising issue.

Thanks so much for your support.