Pyserial string to byte encoding to write to microcontroller

Question

I'm trying to communicate between my PC and a microcontroller (MC). My microcontroller will read using getchar() until 4 characters have been read or it bumps into the characters '\0', '\', or '\r'.

The communication works perfectly fine with hyper-terminal. However, my python script doesn't seem to be sending '\0', '\', or '\r' when encoding an input string and concatenating with one those special characters to it.

command  = input("Enter Command: ")
port.write(bytes(command + '\n', 'UTF-8'))

So if I entered the command x it should send 'x'and'\n' and the MC should stop waiting for more characters to read because of the new line. However, if I enter only x, the MC will wait for 4 more characters to read.
How do I convert my string with the special characters properly to bytes? Thanks.

The MC code is:

buffer[ii] = getchar();

while(buffer[ii] != '\0' && buffer[ii] != '\n' && buffer[ii] != '\r' && ii < 4 - 1)
{
    buffer[++ii] = getchar();
}

HennyH · Accepted Answer · 2013-05-13 03:04:36Z

1

You can convert a string into an array of integers 0 <= N <= 256 by either:

map(ord,command+'\n') or bytearray(command+'\n',"UTF-8")

If you had to write each byte one by one to the port:

>>> for b in bytearray("message\n","UTF-8"):
...     port.write(b)

Should do the trick.

answered May 13, 2013 at 3:04

HennyH

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1 Comment

roverred Over a year ago

Thanks. So I had to send one byte at a time, but add a 10 ms delay as well. Seems like python will send the entire message at a time while hyperterminal sends one byte at a time. getchar() seemed to look at the first char and then the rest of the data was lost with pyserial. One small changes to the for loop code above is b must be converted to a byte first.

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