A parallel port will not be too slow for this, but under normal PC
operation its timing will be too inconsistent. I have tried (and
succeeded) to drive a small linear CCD using a bit banged parallel port,
but using an assembly+C program that took over all interrupts from the OS
(and caused it to lose time etc). Video signal can be generated in the
same way, but it is easier to get an older CGA card that has a RCA B/W
NTSC output jack on it. You may have to run through junk to find one, I
have one and it is irreplaceable.

One thing that can be tried is to make a RS232 port output at least large
characters and bar graphs. Using 256K speed gives about 4 usec per bit
which allows 13 bits in each line (assuming 52 usec visible scan in PAL).
The vertical resolution is 300 lines which is enough for certain bar
graphs and other such applications. I once did all the figuring. I'd use a
PLL built from CMOS chips to generate the H sync signal, by locking to the
312th harmonic of the V signal which was generated by RS232 RTS. This
might even work under some OS as long as you can write the serial
interrupt routine for it (hint hint: open source or open architecture
required). But I never got around to try it out. Note that 312 = (625 -
1)/2 = 256 + 56 ~= 256 + 64 (which simplifies the divider feedback). NTSC
uses 525 lines and you get to do your own numbers. BTW you can make a PLL
for this with a 12 bit PIC ;)

The image will not be interlaced properly and it will have some flicker
unless the PLL generates serration pulses and the computer can delay by
1/2 line in software when appropriate.

hope this helps,

        Peter

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