Re: Anybody with an oscilloscope as an Apple II display?

[ferdimh@gmx.de]

On 26 Mrz., 01:49, "Charlie" <charlieD...@verEYEzon.net> wrote:
> "Michael Black" <et...@FreeNet.Carleton.CA> wrote in message
>
> news:fsbmk3$cgr$1@theodyn.ncf.ca...
>
>
>
> > "Charlie" (charlieD...@verEYEzon.net) writes:
> >> <heuser.mar...@freenet.de> wrote in message
> >>979c1f83-bb91-4cc8-977b-9cacad9a5a55@13g2000hsb.googlegroups.com">news:979c1f83-bb91-4cc8-977b-9cacad9a5a55@13g2000hsb.googlegroups.com...
> >>> Something on the line of this here:
> >>>http://www.youtube.com/watch?v=s1eNjUgaB-g
>
> >>> Maybe not as detailed but is it feasible at all?
>
> >> It is definitely feasible.  Years ago, I had my Apple II output the video
> >> to
> >> a oscilloscope.  Unfortunately, I don't remember how I did it and a
> >> search
> >> of my old notes and documents has turned up empty.  I'm not much of a
> >> hardware guy, so it couldn't have been too difficult.  I probably saw how
> >> to
> >> do it in some magazine article (maybe a Steve Ciarcia article in Byte).
>
> > You were likely using the scope as a monitor.
>
> Yes.  It was just something I tried to see if it would work.
>
>
>
> > So the actual video signal goes to the z axis (that would control the
> > brightness of the trace), the horizontal sync signal to the horizontal
> > input and the vertical sync signal to the vertical input.
>
> > You'd probably need some bits of circuitry.  You could use the scope's
> > sweep to be the horizontal sweep of the "monitor" but you'd need something
> > for the vertical.
>
> I do seem to remember making a small circuit, but I was always playing
> around with stuff hooked up to the Apple so I may be thinking of something
> else.  I normally keep all my notes and/or documentation so it's a little
> frustrating to have to rely on my memory :-)
>
> Charlie

Well, I JUST tried to do it after I read this thread...
If you have an Apple ][/][+ it is possible with a resistor and a
capacitor and nothing else.
If you feed the SYNC signal on pin 19 of Slot 7 through a low-pass
filter, you can get an acceptable vertical sawtooth. with 47kΩ /1μF it
is about 20mVpp which is enough for my scope. You need to wire the low-
pass directly to the BNC input of the scope or it will pick up noise.
Wire the SYNC to the external trigger and adjust to get a raster.
Then wire the video signal to the Z axis. On the Apple ][ it should be
available in a non-inverted form, but in the Apple //e it's only
inverted so I needed one inverter to make it non-inverted.
On my scope it is fairly blurred and dark, but it has already had 20
years of hard use...
40-col Text is barely readable  and the pacman score I yielded was
fairly low...
This has nothing to do with the vector display shown though.

But why shouldn't it be possible?
OUT LDA XVALS,Y      5
        STA DACX           4
        LDA YVALS,Y      5
        STA DACY           4
        INY                      2
        BNE  OUT           3
All done in 23 cycles, which is as fast as the sound card can do it
(23 cycles=22.5 μs->44340 HZ samplerate)
after 256 dots the code would need to modify itself to continue
plotting.
The vector list, however, can't be calculated in real-time but needs
to be stored in RAM before. This limits the Apple ][ to about half a
second of animation before RAM is running out. But with some
compression tricks, more complicated displays could be possible.

Ferdinand