Sending USB commands with Python

[Cameron Simpson]

On 30Aug2012 05:51, Adam W. <AWasilenko at gmail.com> wrote:
| On Thursday, August 30, 2012 12:55:14 AM UTC-4, Dennis Lee Bieber wrote:
| > 	How many bytes did it claim to send?
|
| 11, which is what I expected.  But I changed the byte value to 16
| (because I was having trouble getting single digit hex values working
| in the command) and sent this command:
|
| >>> for x in range(0,500):
| 	ep.write(b'\x16\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF')
| 
| it respond with 500 17's and prints a black bar!  So it looks like whatever concern you had with using encode was coming to fruition.

Yeah. Try 'iso8859-1' instead of 'utf-8'. You want to be not translating
the byte values at all. UTF-8 encodes character values over 127 as multibyte
sequences. ISO8859-1 is a 256 code set that does no translation -
character codes in go directly to byte values out.

You're speaking a binary protocol, not text, so you want a one to one
mapping. Better still would be to be using a bytes I/O layer instead of
one with a text->byte translation; I do not know if the USB library
you're using offers such. So try 'iso8859-1'; at least the translation
is a no-op.

Cheers,
-- 
Cameron Simpson <cs at zip.com.au>

B1FF is an archetype, and all you're showing us is one of the more amusing of
his many instantiations.        - Howard E. Motteler <motteler at umbc.edu>
Ah, perhaps Arthur Clarke anticipated this in his celebrated short story,
"The Nine Million Names Of B1FF"? - Nosy <ataylor at nmsu.edu>