RE: Poll preliminary results...

> Only if you switch the voltage on a capacitor or something (similar to
> the
> Cinematronics design), if you try to draw the lines one step at a time
> you run
> into the same speed issues that have been discussed earlier.
>
Maybe. I don't need to do anything but draw pre-determined pictures of
limited complexity though. I know Eric Smith had a limited function
PIC->Vector tester working a couple years back. There's probably not
enough time to bit-bang serial DAC data though...

> I did figure out at one time that you could do a 1024 x 1024 vector
> generator
> using one of the 50mhz scenix(sp?) PIC clones if you used external
> counters and
> parallel DACs. I think you had something like 15 instructions to do
> the main
> draw loop.
>
For a full DDA probably. This would more likely be a series of loops
that execute sequentially to draw the test patterns only... pseudo code
time:

(draw from upper left corner, to lower left corner, then to lower right
corner...)
        
        counter <- +256
        y_count <- +128
        x_count <- -127
left_side:
        y_count <- y_count -1
        output x_count, y_count
        counter <- counter -1
        if counter >0 goto left_side

        count <- +256
        x_count <- -127
        y_count <- -127
bottom:
        x_count <- x_count +1
        counter <- counter -1
                if counter >0 goto bottom

etc... Maybe have some nop's for timing. The drawing might not be
exactly linear either, but enough to draw some test patterns.

> Since the Cine->WG board would basically be a full vector generator, a
> nice way
> to come up with a vector tester would be simply to drive the digital
> inputs of
> this board with a PIC processor.
>
True. I've got that ISA-Vector Video Card thingy too. (Neil pledged
driver support. ;-)

> >Think it needs three outputs for color? (or just one that
> >you could switch from gun-to-gun? hard to do convergence that way
> >though).
>
> Or three switches that allowed you to control each gun separately...
>
Yeah, I was just seeing if I could weasel out of the extra transistors
and discretes. Actually, with surface mount 2n390x's it doesn't really
take up much room to have full color...

-Clay
Received on Fri Aug 21 17:43:48 1998