Re: MISC video spec (640x480 ?)

[Andrew Sieber <asieber@xxxxxxx>]

> The restrictions applie to NTSC composit video and have to do with the
> color modulation.  NTSC transmits the brightness (luminance) signal
> by amplitude modulation of the carrier wave, and encodes the color
> signal by phase modulation.  The frequency for the color burst signal
> and color phase modulation is provided from an external oscilator.
> The 3.5Mhz signal for color modulation is provided by an external
> 14M oscilator.
> 
> On MuP21 this feature limits the programmability of the video resolution.
> The lumenance and chromanance singals are derived from the same clock and
> the 3.5Mhz is requirement for color modulation and this locks you into
> limited variations on spatial resolution.
It seems to me you could generate any resolution you wanted if you were
willing to sacrifice color.  If you use only black and white, you could
run the external clock at more than 14.3MHz.  You'd then be generating
only lumenance, but no chromanance signal, and since the lumenance does
not have the 3.58MHz dependency, this should work.

--Andrew