[Linux-parport] USB - parallel port converter with individual bit control

Bence Béky bbeky at cfa.harvard.edu
Wed Jun 23 19:19:35 EDT 2010


I need help to control home-brew equipment via an USB - parallel port
converter. Any ideas or recommendations are welcome.

In detail: We have a bunch of remote controlled telescopes with
control electronics that we have developed ourselves. Most of the
functionality -- stepper motor driving, ramping, end position sensor
handling -- is implemented in the control computers via parallel port,
and we use every bit available. Also we extensively use hardware
interrupts to react to input bit changes real-time. We would, however,
like to get rid of PCI parallel port cards as it is not clear whether
we can still get spare parts (such cards, computers with PCI ports,
parallel port surcharge isolators etc) in five years from now. Using
USB adapters seems like a good idea.

The main problem is that one cannot find out what chip a certain USB
parallel port converter product uses without buying it. I bought three
of them, one has MosChip 9710:7705, that does not seem to be supported
at all; the other two have 067b:2305 PL2305, that is supported by
usblp but only in IEEE1284 mode. The datasheet of PL2305, rev1.1
2002-08-01 mentions vendor-specific commands that supposedly support
the operation we want, but is not specific about it. This section is
removed from the datasheet in rev1.2 2006-09-26.

I also found that there is a driver for Lucent USS720, that uses that
chip in register mode and creates a parport device.

Any of the following would solve our problems with more or less work:

 - is anyone aware of a driver for PL2305 that uses
parport_register_port and thus creates /dev/parport? device,

 - does anyone have a datasheet (maybe rev1.1E 2006-06-31) or
documentation or specification of PL2305 "vendor-specific device
requests" or any information that would clarify that PL2305 in fact
does not support what we want,

 - does anyone have any information about commercially available USB -
parallel port devices that sport Lucent USS720, or any other chip that
is capable of what we are looking for,

 - does anyone have experience with USB based industrial I/O devices
that we could use?

I didn't find relevant information in the linux-parport archives or on
any forums. Your help is very much appreciated.

Thank you,

Bence Béky
HAT project
Harvard--Smithsonian Center for Astrophysics

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