Re: AppleColor Composite Monitors discussion

[MdntTrain <js@cimmeri.com>]

> Although it certainly doesn't hurt to have a fine shadow mask pitch,
> 0.52mm is really not very fine.  The CRT was chosen to support just
> enough resolution that it's tolerable to view 80-column text on it.
>
> It's pretty good for a TV CRT, but not very good for a color monitor.

Yeah, it's definitely not as good as the IIgs RGB monitor's .31 or .
35? pitch (for 12") for around 650 trio stripes... but on the other
hand RGB arcade monitors of that period were at .66 for 13" and .82
for 19" so it's not too shabby.


> What makes this monitor unique among composite monitors, and able
> to display readable 80-column text at all, is that it has a switchable
> bandwidth luminance channel that goes into high bandwidth mode when in
> monochrome mode.

Yes, I notice it does that automatically with the IIe/IIgs, but
earlier I have to press the button.

Related to this luminance bandwidth topic, we determined awhile back
that in Apple II 40 col text and HGR, the "dot clock" was 7mhz..
meaning that dots are being sent out at that rate.   For 80 col text
or DHGR, the dot clock would be 14mhz.   Further, you discovered that
for IIgs 320 mode, the rate was 8mhz, and for 640, 16mhz.

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?

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?

Cool stuff.  Thank you Michael!
~ J