Re: IIgs RGB to VGA experiment

["David Wilson" <mcs6502@gmail.com>]

js@cimmeri.com wrote:
> So my questions are:
> - Does the IIgs itself (as opposed to its mate monitor input) put out
> 15.734khz horiz scan?   If so, why 16hz less than the standard
> 15.75khz?   Does this slight difference make any difference at all?  In
> other words, can a 15.734khz source drive a 15.75khz monitor?      I
> notice that the Commodore 1084 monitor I have is also 15.734khz input
> for its RGB jack.

15750 Hz was the standard horizontal sync frequency for monochrome TV
(along with 60Hz vertical sync). When NTSC color was developed the
frequency had to be shifted slightly to ensure that the color signals
fitted into gaps in the frequency spectrum. Thus you now have 15734 Hz
and 59.94 Hz respectively.

The Apple II/II+/IIe all use a 14318180 Hz master clock which is
divided by 14 to get one character cell and by a further 65+2/14 to
give 15699.8 Hz.

I think that the IIgs timing is the same but do not have my reference
books to hand.