Read and write to port with unit8 format?

Question

I have Matlab code that communicates over serial port, and I am trying to translate the code into python, however I am not getting the same "read" messages.

Here is the matlab code:

s = serial('COM3','BaudRate',115200,'InputBufferSize',1e6,'Timeout',2);  %OPEN COM PORT
fopen(s);
string=[];
while(length(st)<1)
    fwrite(s,30,'uint8');   %REQUEST CONNECTION STRING
    pause(0.1);
    st = fread(s,5);  %READ CONNECTION (5BYTES, "Ready")
    disp(st)
end
fwrite(s,18,'uint8');   % START ACQUISITION

while(1)
    st(1:131) = fread(s,131); .....
    disp(st)

OUT:

%first disp(st)
    82
   101
    97
   100
   121

%from disp(st) second time
  106
    85
   106
    59
   106
    61
   106
     0
   106...

Here is my attempt of python code:

# Open serial - 
import serial 
import time

s = serial.Serial('COM3', baudrate=115200, timeout=2 )
s.set_buffer_size(rx_size = 1000000, tx_size = 1000000)
 #serieal is open
print ("serial is open: ", s.isOpen())

s.write(30) #request connection string
time.sleep(0.1)
string = s.read(5) #read connection string (5 BYTESm "Ready)
print (string)

# start aquisition 
s.write(18) #request connection string
print (s.read(131))

however the output is, OUT:

serial is open:  True
b'Uj.jg'
b'jVj3j-i\xefjOj8jajJj"i\xb8j\x19j4j,j\x17\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00j\x9aj\x9aj\x8djfjkj/j\xa0j\x97jbjKj#i\xb9j\x1bj5j-j\x19\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00/\xaaUj\xe5j\xb7'

As you can see they aren't the same, so:

1. How do I send via pyserial a 'uint8' encoded number like in matlabs: fwrite(s,30,'uint8');
2. How do I read and display from pyserial similar to matlabs: st = fread(s,5);

Answer 1

How do I read and display from pyserial similar to matlabs: st = fread(s,5);

uint8 means 8-bit number. So 1 byte.

In python, you get a bytes object which is a sequence of bytes. You can iterate over it to get each value. - Which is exactly what you want, because that would be a value of one byte, 0-255

first = b'Uj.jg'
for i in first:
    print(i)

This gives you:

85
106
46
106
103

How do I send via pyserial a 'uint8' encoded number like in matlabs: fwrite(s,30,'uint8');

You can convert your int to bytes object using int.to_bytes:

print((30).to_bytes(1, byteorder="big"))

Results in

b'\x1e'

First argument is number of bytes - in our case 1. Second argument is byte order - which is useless when we use 1 byte but it's still required.

So what you had as s.write(30) will be

s.write(b'\x1e')

or to keep the "30" thing visible just directly paste the conversion:

s.write((30).to_bytes(1, byteorder="big"))

Same for sending 18: s.write((18).to_bytes(1, byteorder="big"))