hexadecimal numbers over UART

[BL007]

Hello,


how can I send hexadecimal numbers via UART?
If I try 'hex(0xEE)' then I get an error from µPython. '238' also. 'bytes([283])' or 'bytes([0xEE)' sends a 0x00.

I use the UART lib from µPython.

[cgglzpy]

Hi BL007

What you are looking for is 'struct' see: http://docs.micropython.org/en/latest/l ... truct.html and https://docs.python.org/3/library/struct.html

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>>> import struct
>>> struct.pack('B', 238)
b'\xee'
>>> struct.pack('B', 0xEE)
b'\xee'

To decode

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>>> struct.unpack('B', b'\xee')
(238,)
>>> val,=struct.unpack('B', b'\xee')
>>> val
238

Just be aware of the type of numbers (signed, integer/float, size...) you want to send. So adjust the encoding/decoding format and that's it.

[BL007]

Thanks!
The conversion from str to hex is clear. It works with de-/encode() also.

But the UART.write() sends ASCII only.

uart.write(b'\xAA')
>>> 0x41
0x41

If I want send 238 as an integer, the µPython brings error. The question ist, can the UART class works with strings only?

[Roberthh]

uart.write() works with objects with buffer protocol, meaning strings, bytes, bytearrays, etc. But not e.g. with single integers, floats, etc. If you want to send the number 238 as the three digit ASCII string "238", you have to convert that first, like with str() or any formatting method.

[pythoncoder]

Also see the int.to_bytes and int.from_bytes methods https://docs.python.org/3/library/stdty ... t.to_bytes.

[BL007]

uart.write(b'\xAA')
>>> 0x41
0x41

That was wrong from me. I recieve the dates from the UART in a PIC. There I forgot that I need a b'\x01' before the actual data. If I send

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uart.write(b'\x01\xAA)

then I recieved 0xAA in the PIC.


That's all good and chic. But it's not the solution of my problem.

I have strings like '53006400C845'. There are 6 btyes. But in a string. I tought I begin to try with one byte. Because 'EE'.
struct.pack need a int and makes a byte. I have a string.
str.encode() makes the ASCII-Code of the letters of chars.

Wich function makes from '53006400C845' => b'\53\00\64\00\C8\45' or leastways from '53' => b'x53'?

[Roberthh]

Use ubinascii.unhexlify()

[BL007]

Thanks!

But that's not it.

This makes the ASCII-Code of the letters. From 'EE' => 4545
I need b'\xee'.

[Roberthh]

You tried hexlify instead of unhexlify.

[BL007]

I wrote a function.

This works.

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def str2byte16(strdata):
    from struct import pack
    num8 = str2byte8(strdata[0])
    num16  = str2byte8(strdata[1])
    data16 = (num16 * 16) + num8
    bytedata16 = pack('B',data16)
    return bytedata16 

def str2byte8(strdata):
    numchar = ord(strdata[0]) 
    if numchar > 47 and numchar < 58:
        num8 = numchar - 48
    else:
        if numchar > 64 and numchar < 71:
            num8 = numchar - 55
        else:
            num8 = numchar - 87
    return num8