How to understand the received bytes of ser.read?

[pf2022]

Hello,

I'm using a function ser.read (from PySerial) to read a sequence of 2000 bytes from a microcontroller. Two received bytes in a sequence are actually two bytes of uint16 data which are combined in python script (so in Python these sequence of 2000 bytes are combined into 1000 uint16_t data), but that's not important here.

I have a problem with understanding the received bytes of ser.read form the figure bellow (print(s))? Please click the the gray rectangle bellow to see the figure.

   


After printing out data received with ser.read with print(s) I can see strange printout. I would expect that each byte is in a form like \x04, but at the beginning I can see the form like \x04J, the listing also start with G\04F\...? So at the beginning of the figure I can see that there are three numbers or a strange (not hex) characters instead of two hex numbers (equals one byte)?

The code is here:

import serial
import numpy as np
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.widgets import Slider, Button, RadioButtons
from scipy.signal import savgol_filter

import matplotlib.pyplot as plt
from pylab import *
import numpy as np

ser = serial.Serial('COM13', 921600, timeout=None,parity=serial.PARITY_NONE)
fig = plt.figure()


while True:

    ser.flush()

    x = np.linspace(0, 1000, 1000)

    s = ser.read(2000)
    y1 = np.frombuffer(s, np.uint16)  #y ... np array...
    
    plt.plot(x,y1,'-*',label='graf 1')  

    plt.xlabel('TIME')
    plt.ylabel('ADC current')
    plt.title('Solenoid I/t')

    legend()

    plt.show()

    print(s)

ser.close()             # close port

I will be grateful for any help
Ernest

Larz60+ write Mar-24-2022, 11:16 AM:
Fixed BBCode tags.

[Larz60+]

can you find any help here: https://github.com/pyserial/pyserial/tre...r/examples ?

[Gribouillis]

This is because Python shows bytes corresponding to printable ascii characters as characters, as well as the escape sequences \t \n \r

>>> bytes(range(256))
b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
>>> for i in range(16):
...     print(bytes(range(16 * i, 16 * i + 16)))
... 
b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'
b'\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f'
b' !"#$%&\'()*+,-./'
b'0123456789:;<=>?'
b'@ABCDEFGHIJKLMNO'
b'PQRSTUVWXYZ[\\]^_'
b'`abcdefghijklmno'
b'pqrstuvwxyz{|}~\x7f'
b'\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f'
b'\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f'
b'\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf'
b'\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf'
b'\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf'
b'\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf'
b'\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef'
b'\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
>>> 

so G is \x47 and F is \x46 for example.

[pf2022]

Thank you very much!
Ernest