Hi,
        Let me clarify the application a bit.  The PIC based unit is transmitting
video from a CCD (a CCD for a astronomical camera) to computers that someone
may already have, a printer port or USB.  The transfer time must be
minimized to get as fast a frame rate as possible.  The only viable
alternative to the parallel ports is a full speed USB interface.  I've been
looking at the new PIC micro with USB, but it seems to be a low speed USB
interface suitable for a mouse or keyboard.  The second generation unit will
most likely be full speed USB.  As the project stands now, I'm getting a 4
second transfer via the parallel port.  With the current hardware, A/D
converter, signal conditioning, the best rate I could expect is about 15usec
per pixel.  Right now I'm getting a little less than 30 usec.  The delays
are now in the bit toggling and reading by the PC from the parallel port.
The frame transfer time of 4 seconds vs 2 seconds is not really important
when capturing the imaged frame ( an extra 2 seconds after a image
integration time of 10 minutes doesn't matter much), but it is important
when in the focusing mode.  While focusing you need to see the image quickly
as you turn the focus knob.

Again, thanks to you all for your help and suggestions.

Regards,
Dave

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