Crazy Monitor idea for old Home Computers

Eric Smith eric at
Mon Apr 25 04:44:46 CDT 2005

> I thought the composite output on a IIgs was mono only.  To get color you
> have to use the RGB output.  To run it on a VGA monitor I'd use a scan
> doubler such as the Micomsoft XRGB-2.

No, the IIgs has color on the composite output.  Perhaps you're thinking
of the Apple III, which did not.

The IIgs uses a Motorola MC1377 color video encoder chip to produce
composite color video from the RGB outputs of its display chip.

The normal video output of all Apple II models does not really meet
NTSC spec, so some devices will have trouble with it.  In particular,
each horizontal line is supposed to have exactly 227.5 cycles of the
color carrier, but in an Apple II it takes 228.

If you have the video overlay card, that produces proper NTSC output.

There was an amazing hack for the original II/II+ to generate
broadcast-quality NTSC video.  It was a product from Video Associate
Labs called the VB3 Microkeyer.  There was a huge analog board that
sat over the power supply, and a digital board that plugged into
a slot.  You removed about eight of the TTL chips from the Apple II
logic board and replaced them with ribbon cables to the digital board,
and there was a wider ribbon cable running from that board to the
analog board.  The college television studio had one, and I wrote
software for it to perform various wipes.

In addition to fixing the Apple II's video output to meet NTSC spec,
it also added a new hires display mode that scanned memory in a
completely linear order, instead of the usual interleaved fashion.
This made writing software for wipes somewhat easier.


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