USB to parallel

A legacy application (not a simple parallel printer) that assumed that it was interfaced to a genuine hardware parallel port at 0x378 will almost certainly not work with a USB connection in the middle. Things like parallel port based device programmers don't translate well to an intermediate packet based layer.

It might be possible to come up with a way to fool a particular application into running over a USB-parallel port. Designing an adapter that supported all third party applications (which will include some that were written back in the days of MS-DOS and 5 1/4" floppies) is ... challenging.

Rich Webb ha scritto:

Ok, thank you very much for your answer. Furthermore, the main application should be a stepper motor driver: I bet the USB device can't handle the clock rate as accurate as the hardware parallel port can.

Marco

What part of a USB port is not hardware? Also, one could easily write the stepper motor app and design the I/O interface such that no difference could be detected.

Archimedes' Lever ha scritto:

I'm talking about the USB protocol.

Of course. But I need to interface existing apps.

Marco

FTDI also make FT245* devices that have a parallel interface (no, it's not exactly equivalent to a PC parallel port (IEEE 1284) but it does give you the ability to bit-bash several I/O lines). Their newer devices, e.g. FT2232D, can be run in a number of modes, allowing them to emulate both the '245 and the '232 parts.

The very newest FTDI parts, e.g. FT2232H, use USB2.0 which might allay some of your timing concerns.

Regards, Allan

For a given application it may be possible to implement a USB solution, particularly if you're comfortable with sticking a microcontroller "in the middle" to handle the low-level timing issues. That still may not fly if the host application on the PC side expects to have well-defined command/response cycles on the I/O lines.

An option may be to try a PCMCIA parallel port. These could be (note: not all are) identical to a legacy hardware port. Or an expansion card, if you're running a desktop or PC/104 unit.

Rich Webb ha scritto:

Thank you again. Marco

if you can put the USB in isochronous mode it will do it better than a hardware parallel port can.