Vector Imagery

[Roy J. Tellason]

On Tuesday 04 July 2006 03:51 pm, Josh Dersch wrote:
> Brad Parker wrote:
> > I would guess that a simple parallel port adc on a PC could do very
> > well displaying a reasonable number of dots on a scope with intensity
> > control...  not very impressive given what fpga's do now shading
> > polygons, but fun none the less.
>
> A couple of years ago I tried this -- I built two very (very) simple
> parallel-port DACs (one for X, the other for Y) and I had them connected
> to linux machine with two parallel ports.  I wrote a small test app to
> rapidly write data to the output pins on the parallel ports.  Plotting
> points on the oscilloscope worked OK (aside from the poor precision of
> my DACs), but drawing arbitrary vectors seemed to be impossible because
> I couldn't figure out a way to change the data sent to the parallel
> ports for X and Y at /exactly/ the same time.  Since X would be changed
> slightly before Y (or vice versa) I'd get a stairstep effect instead of
> a single line from point A to B.
>
> Maybe a faster machine would be able to reduce this effect (I was using
> a Pentium Pro 200), or clever use of DMA...

Or maybe using some outboard latches and those strobe pins on the port?  Or 
something like that anyhow...

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