在 raspberry pi 3B 上的 python 代码中使用 python 库 pymodbus2.5.3 将寄存器解码为 32 位浮点大端

Question

我正在尝试在我的 raspberry pi 3B 上获取使用 modbus rtu 通信协议的传感器变送器的数据流。我可以使用 pymodbus2.5.3 库获取数据。为此，我使用此代码：

from pymodbus.client.sync import ModbusSerialClient # Import the pymodbus library part for syncronous master (=client)

client = ModbusSerialClient(
    method='rtu', #Modbus Modus = RTU = via USB & RS485
    port='/dev/ttyUSB0', #Connected over ttyUSB0, not AMA0
    baudrate=19200, #Baudrate was changed from 38400 to 19200
    timeout=3, #
    parity='N', #Parity = None
    stopbits=2, #Bites was changed from 1 to 2
    bytesize=8 #
)

if client.connect():  # Trying to connect to Modbus Server/Slave
    #Reading from a holding register
    res = client.read_holding_registers(address=100, count=8, unit=1) #Startregister = 100, Registers to be read = 8, Answer size = 1 byte



    if not res.isError(): #If Registers don't show Error
        print(res.registers) #Print content of registers
    else:
        print(res) #Print Error Message, for meaning look at (insert git hub)

else: #If not able to connect, do this
    print('Cannot connect to the Transmitter M80 SM and Sensor InPro 5000i.')
    print('Please check the following things:')
    print('Does the RS485-to-USB Adapter have power? Which LEDs are active?')
    print('Are the cables connected correctly?')

并得到以下输出：

[15872, 17996, 16828, 15728, 16283, 45436, 16355, 63231]

在 Modbus 轮询和从站程序的帮助下，我知道这些结果应该被解码为： [0.125268, --, 23.53, --, 1.21094, --, 1.77344, --]

为了获得正确的结果，我尝试了 pymodbus github 建议的命令 .decode():

res.decode(word_order = little, byte_order = little, formatters = float64)

[我知道这些不是必需的选项，但我复制了建议的 github 代码以检查它是否有效。]

将代码段放入代码后，更改的部分如下所示：

    if not res.isError(): #If Registers don't show Error
        res.decode(word_order = little, byte_order = little, formatters = float64)
        print(res.registers) #Print content of registers
    else:
        print(res) #Print Error Message, for meaning look at (insert git hub)

当我运行这段代码时，我得到以下输出，可以追溯到解码段：

NameError: name 'little' is not defined

在此之后，我还导入了 pymodbus 部分翻译。但它显示相同的输出。

如何解码传入的数据？

Answer 1

您可以使用 BinaryPayloadDecoder 来帮助解码您的负载，这是一个简化的示例，如果需要，请更改 Endian.Big 和 Endian.Little。

if client.connect():  # Trying to connect to Modbus Server/Slave
    #Reading from a holding register
    res = client.read_holding_registers(address=100, count=8, unit=1) #Startregister = 100, Registers to be read = 8, Answer size = 1 byte

    # ====== added code start ======
    decoder = BinaryPayloadDecoder.fromRegisters(res.registers, Endian.Little, wordorder=Endian.Little)
    first_reading = decoder.decode_32bit_float()
    second_reading = decoder.decode_32bit_float()
    # ====== added code end ======

    if not res.isError(): #If Registers don't show Error
        print(res.registers) #Print content of registers
    else:
        print(res) #Print Error Message, for meaning look at (insert git hub)

记得在顶部导入 from pymodbus.payload import BinaryPayloadDecoder 并在最终代码中添加必要的异常处理程序。

Reference document: https://pymodbus.readthedocs.io/en/latest/source/library/pymodbus.html#pymodbus.payload.BinaryPayloadDecoder

在 raspberry pi 3B 上的 python 代码中使用 python 库 pymodbus2.5.3 将寄存器解码为 32 位浮点大端

decode register to 32bit float big endian in python code on raspberry pi 3B with python library pymodbus2.5.3

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