Vector Graphics?

[Martin Giese]

Last summer, my wife found a cheap piece of kit at a flea market she thought I might want.  Turned out to be a Tek 465B oscilloscope, and it’s still (mostly) working. I’m determined to have as much fun with it as possible, for as long as it survives.

One of the things that are really great about CRT scopes is the zero latency XY mode. Perfect for Oscilloscope Music for instance.

And that got me thinking: has anyone ever made a Vector Graphics display for the Z80 to talk to?  I.e. a peripheral that will display line graphics on an oscilloscope?

I found a project using a computer and its sound card here – but I fear any approach where the Z80 speaks to a DAC live in order to generate the signals would leave no time for the Z80 to do anything else. Some kind of co-processor repeatedly working its way through a “display list” seems to be the way to go.

Martin

[Matt Callow]

There  was an old project in ETI to do this back on the 80s on the ZX81. I never built it, but it has always fascinated me.

 https://worldradiohistory.com/UK/Electronics-Today-UK/80s/Electronics-Today-1984-01.pdf#search=%22vector%22

Matt 

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[Mark T]

You might find this interesting, its another of Karen Orton’s projects.
https://vintage-radio.net/forum/showthread.php?t=149829

[Matt Callow]

That's an interesting circuit. Much simpler than the ETI one, but it will rely on accurate timing from the CPU. 

It also doesn't need a Z input to blank the display (instead moving the Y axis off-screen I think)

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[Martin Giese]

Thanks for those pointers!  Two very interesting designs.

Both get by fine without the hardware looping through a display list, that’s encouraging.

Indeed, Orton’s approach is very minimalistic, replacing the DAC by pulse width output.  As Matt points out, this will leave a lot of the work to the CPU, and require precise timing.

The ETI design has a status bit that will be read by the CPU to find out if the peripheral is done with a line.  I think this could be modified to raise an interrupt, so the interrupt handler can deal with walking through the list of line segments to be displayed.

Martin

[Ed Silky]

In the mid-80's the VecTrex game system came out using CRT vector graphics. I don't recall what CPU it used, but you might look into it and how it generated the signals to drive the display.

-Ed

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[Phil]

I had a Vectrex back then.  It used a 6809 controlling analog circuits to drive high voltage to the yoke deflection coils on a 9" black and white TV tube. 

[Ed Silky]

Thanks Phil. A friend had one, so I played it a fair amount, but he wouldn't let me take it apart. ;-)

@Martin, since you are driving an oscilloscope you don't have to worry about high-voltage. I haven't done a lot with a 6809, but I think it might have a few things that make it a little better for the job than the Z80, but now the Z80 has a significant clock speed edge over the 6809 in a VecTrex, so you might look into the design and see if there are any good hints on things you could try.

-Ed

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