Re: Kaypro dead.. how to use the monitor?


"Ron Kneusel" <oneelkruns@xxxxxxxxxxx> wrote in message
news:1151870690.273753.130680@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I have a dead (highly unreliable) Kaypro II. I asked about it
here a few months ago but now it is really kaput. So, I'm
thinking to use the case and monitor in some way. From
looking at the Kaypro technical manual I know which pins of
which jumper control the horizontal and vertical sync. So,
here are my two questions:

1. What do I need to do to be able to feed a composite video
signal into the monitor?
2. How could one control the TTL video with a microcontroller?

If I can feed a composite video signal in I might put an
Apple IIgs motherboard into the case. If it is too hard to
get composite working (I'm an electronics newbie) then it
would be fun to control the video with some sort of PIC,
perhaps to make a sinple Pong-like game (yes, I know others
have done this already).

Does anyone have any insights? All replies much appreciated.

Ron

The synch information in a composite video signal is usually
carried in the negative tips of the wave form. Capturing it
involves "clamping" the tips (with a capacitor and diode) to
remove any A.C. variations, and "slicing" the pulses with a
comparator (which may be just an un-biased transistor fed from
a resistor to its base).

The horizontal and vertical portions are separated by a
"one-shot" edge-triggered pulse timer, with some "AND" gates,
to distinguish short pulses from long. On the other hand, it
may be enough to deliver the combined synch signal to both
the monitor's synch inputs, and see if the monitor can
separate them. In either case, the polarity(s) of the signals
may be important (mostly high vs. mostly low).

I think some CGA cards could be set for composite video out,
but still generated separate synch and video on the digital
interface.

To generate the pulses required rather precise and very
repeatable timing. It is therefore usually created with
hardware, consisting of a crystal based clock and a series
of counters (plus a few gates). The schematics for the
Kaypro give one such design, of course :-).

You need to generate around 15,750 horizontal lines per
second, with 2 vertical pulses every 525 lines. For normal
interlace, one usually starts with at least 31,500 pulses
per second, and separate dividers (/2 and /525) to get the
interlace phasing correct. The Kaypro monitor will probably
look better with non-interlaced timing, say, 1 vertical
pulse every 264 horizontal lines. It is sometimes important
to lock the synch signals to the local power line frequency,
to hide any "beating" with the vertical rate.

A microprocessor with a hardware timer for the horizontal
pulses and an interrupt-driven routine to set the vertical
pulses might be easy enough, but you would still be faced
with generating the video pulses in the proper
synchronization.

A pong type game would generally use several more hardware
timers for the horizontal positions of the paddles and ball,
but might get by with a per-line interrupt for all the
vertical timing. In that case, some external gates for
mixing the horizontal and vertical info might still be needed.

The Timex-Sinclare ZX80/81 had a hardware+software scheme
that accomplished all this by force-feeding the CPU
hardware-controlled op-codes during the video display phase.

P.S. What is this "unreliability" that leaves you thinking
that the video is still good? Maybe you have a problem
with the +5V supply that should be fixed instead?


.

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