Re: AppleColor Composite Monitors discussion

[David Wilson <mcs6502@gmail.com>]

On Mar 5, 3:15 am, MdntTrain <j...@cimmeri.com> wrote:
> Two questions about this.  1) How would someone with an oscilloscope
> go about verifying these dot clock rates, say for starters just on a
> IIe?   Obviously, the scope gets hooked up to the video out and the
> timings set to see one horizontal line.. but what would we need to
> have on the screen and then look for in the waveform to count this dot
> clock?

I would fill the scree with alternating black and white vertical
lines. I would then zoom in until I could measure the width of one of
these lines in nanoseconds - invert this and you have frequency.

> 2) How does dot clock relate to needed bandwidth?   If a 14mhz dot
> clock is used for 80 columns, how does the Applecolor or IIgs RGB
> monitor handle that with an 8mhz bandwidth?    Is it because of half
> cycles, such that 14mhz requires a 7mhz analog bandwidth?

Yes, the dot clock is twice the frequency of the waveform generated by
alternating black and white pixels.