如何解码 python 中的 HEX 和 ASCII 数据？

Question

import serial
from time import sleep

t = serial.Serial(
    "/dev/serial0", 19200, parity=serial.PARITY_EVEN,
    stopbits=serial.STOPBITES_ONE, timeout=0.5
)
cw = [0x01, 0x03, 0x00, 0x00, 0x03, 0x05, 0xCB]
t.write(serial.to_bytes(cw))
rx = t.read()
sleep(0.03)
data = t.inWaiting()
rx += t.read(rx)
print(rx)

This is the code I'm using and the output for rx is b'\x01\x03\x06\x00\x07\x01,\x00\x00T\x80' .

And the format of decoding it is 01 03 06 + voltage higher byte + voltage lower byte + current higher byte + current lower byte + status high + low + crc + parity.

How can I decode the voltage and current? I think it is in hex and ascii format.

Answer 1

There are a couple of ways to do this depending on the context this is being used in. There is the Python struct library and there is the from_bytes int class method.

The data is in little endian format because the higher byte is before the lower byte. I am also assuming that these values can be signed.

Examples of how to do this:

>>> rx = b'\x01\x03\x06\x00\x07\x01,\x00\x00T\x80'
>>> import struct
>>> voltage, current = struct.unpack('<3xhh4x', rx)
>>> print(voltage)
1792
>>> print(current)
11265
>>> voltage2 = int.from_bytes(rx[3:5], 'little', signed=True)
>>> current2 = int.from_bytes(rx[5:7], 'little', signed=True)
>>> print(voltage2)
1792
>>> print(current2)
11265

Looking at the values it might be that the values need to have the decimal point moved by a couple of places if you were expecting approximately 18 volts. eg

>>> voltage * 10**-2
17.92