负数应该如何在 pymodbus 输入寄存器中表示？

Question

我想将负数分配给 pymodbus 异步服务器中的输入寄存器。我有一个名为 PQV 的 5 元素数组，其中包含数量级从 0 到 300 的数字，但有些元素是负数

PQV=[145, -210, 54, 187, -10]

我使用下面的代码将 PQV 分配给从地址 0 开始的输入寄存器（寄存器 4）。我尝试将 65536 添加到所有负数，但这没有用。

如何调节数组 PQV 的负元素以供 pymodbus 接受？

context[slave_id].setValues(4, 0, PQV)

Answer 1

在写入数据存储之前，浮点数将以 IEEE-754 十六进制格式表示。你可以做这样的事情来实现它。

# Import BinaryPayloadBuilder and Endian
from pymodbus.payload import BinaryPayloadBuilder, Endian
# Create the builder, Use the correct endians for word and byte
builder = BinaryPayloadBuilder(byteorder=Endian.Big, wordorder=Endian.Big)

在你的更新函数中

busvoltages = [120.0, 501.3, -65.2, 140.3, -202.4]
builder.reset() # Reset Old entries
for vol in busvoltages:
    builder.add_32bit_float(vol)
payload = builder.to_registers()   # Convert to int values
# payload will have these values [17136, 0, 17402, 42598, 49794, 26214, 17164, 19661, 49994, 26214]
context[slave_id].setValues(2, 0, payload)  # write to datablock

当您读回这些值时，您将得到原始 int 值。您必须使用 BinaryPayloadDecoder

将它们转换回浮点数

>>> from pymodbus.payload import BinaryPayloadDecoder, Endian
>>> r = client.read_input_registers(0, 10, unit=1)
# Use the same byte and wordorders
>>> d = BinaryPayloadDecoder.fromRegisters(r.registers, byteorder=Endian.Big, wordorder=Endian.Big)
>>> d.decode_32bit_float()
120.0
>>> d.decode_32bit_float()
501.29998779296875
>>> d.decode_32bit_float()
-65.19999694824219
>>> d.decode_32bit_float()
140.3000030517578
>>> d.decode_32bit_float()
-202.39999389648438
>>> # Further reads after the registers are exhausted will throw struct error
>>> d.decode_32bit_float()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/sanjay/.virtualenvs/be3/lib/python3.6/site-packages/pymodbus/payload.py", line 440, in decode_32bit_float
    handle = self._unpack_words(fstring, handle)
  File "/Users/sanjay/.virtualenvs/be3/lib/python3.6/site-packages/pymodbus/payload.py", line 336, in _unpack_words
    handle = unpack(up, handle)
struct.error: unpack requires a buffer of 4 bytes
>>>

希望对您有所帮助。

负数应该如何在 pymodbus 输入寄存器中表示？

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