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Newsgroups: comp.lang.python
Date: Wed, 29 Aug 2012 14:21:30 -0700 (PDT)
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Subject: Re: Sending USB commands with Python
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Xref: csiph.com comp.lang.python:28072

On Wednesday, August 29, 2012 4:09:49 PM UTC-4, Dennis Lee Bieber wrote:
>
> 	Don't the commands require an <esc> character? "\x1BA" (or
>    "\x1B\x41")
>=20
> 	OTOH, if the <esc> is issued behind the scenes,

I'm not sure which esc char it is asking for, I don't think libusb is provi=
ding its own, and it seems like the one you suggested isn't what it wants e=
ither..

>  ... and you do not need to issue some sort of read()
> the "2" you are seeing is the "number of bytes written";
>=20
> you need to issue a read request to retrieve the returned printer
>=20
> status.
>=20

You are correct about the 2 being the number of bytes written.  However whe=
n I issue a read command I get:

>>> ep.write('\x1BA')
4
>>> ep.read(1)
Traceback (most recent call last):
  File "<pyshell#75>", line 1, in <module>
    ep.read(1)
  File "C:\Python32\lib\site-packages\usb\core.py", line 301, in read
    return self.device.read(self.bEndpointAddress, size, self.interface, ti=
meout)
  File "C:\Python32\lib\site-packages\usb\core.py", line 654, in read
    self.__get_timeout(timeout)
  File "C:\Python32\lib\site-packages\usb\backend\libusb01.py", line 483, i=
n bulk_read
    timeout)
  File "C:\Python32\lib\site-packages\usb\backend\libusb01.py", line 568, i=
n __read
    timeout
  File "C:\Python32\lib\site-packages\usb\backend\libusb01.py", line 384, i=
n _check
    raise USBError(errmsg, ret)
usb.core.USBError: [Errno None] b'libusb0-dll:err [_usb_setup_async] invali=
d endpoint 0x02\n'

Avoiding the read command all together I should be able to write "<esc> E" =
and have it feed some paper, which it is not doing, so obviously there is m=
ore to uncover.  That said I feel this endeavor has evolved and is no longe=
r pertinent to the Python group so I will let you guys off the hook on this=
 (although responses/suggestions are still welcome).

Thanks for all your help!