J. L. Trantham  wrote:
> Is there a way to connect a parallel port to a computer via USB?  Not a
> device that shows up as 'USB Print Support' but, instead, shows up in Device
> Manager as an LPT port?  I have been able to do it via PCMCIA to Parallel
> Port adapters but I have never found a USB device that would do this.

Nope. Look at how the original PC LPT port works -- it's basically a buffer chip or two, connected to some address decoders, sitting at a particular spot (0x378) on the CPU's I/O bus. There's simply no way to abstract that -- it'd be like asking for USB RAM or a USB BIOS chip. As computers moved away from ISA, that I/O bus has changed somewhat in appearance; these days it exists almost solely within the southbridge chip and then gets squeezed across an LPC link to a super I/O chip, where the legacy peripherals live. It doesn't leave the motherboard.

Software that writes to a lineprinter using the BIOS printer calls, can easily be hooked and redirected. The DOS NET program has done this for decades, as a way to use network printers. But your parallel-port programmer isn't acting like a printer, so the software isn't printing to it -- it's treating the LPT port as a generic 8-bit parallel I/O port, and bit-banging arbitrary signals over it.

Software written to bitbang the port will have to be rewritten to use some other form of I/O. For the typical cases of bitbang interfacing, the FT245R is a very capable little chip, and can be dropped in place of the parallel port, to talk to legacy hardware. It just needs new software to take those raw IN and OUT instructions and fire them over an abstraction layer, which will pass them through the USB stack and out to the device. 

There is an exception -- If you're running legacy software under a modern OS that prevents raw hardware I/O anyway, it's possible to hook those IN and OUT instructions, and write a generic driver that passes the traffic over USB. It's slow, unstable, and basically a miracle if it works. But it's worth a try:
http://www-user.tu-chemnitz.de/~heha/bastelecke/Rund%20um%20den%20PC/USB2LPT/index.html.en

Short of that, your best bet is an old Thinkpad with a hardware parallel port. 

Good luck!
-Nathaniel-

