ferdimh{at}gmx.de wrote:
> In the Apple ][ the long cycle is used to maintain a constant
> relationship between COLOR REFERENCE and the horizontal scans. I'm
> just wondering why a constant phase relationship is needed. If there
> was no long cycle, the COLOR REFERENCE would toggle each line, as
> intended by the NTSC standard. Some modifications would be necessary
> though:
> The vertical counter needs to be synchronized to the alternating COLOR
> REFERENCE phase. I would feed COLOR REFERENCE to D13-6 (see
> Understanding the Apple ][ page 3-14), so that the counter latches the
> state of COLOR REFERENCE when preset instead of toggling before every
> preset.
> The H0 signal fed to A8-14 (page 8-12) needs to be XORed with VA.
> In HIRES mode programming needs to be changed to compensate for the
> alternating phase relations.
> I'd expect better picture quality because straight vertical lines
> would not be colored in one color but alternating green/red or blue/
> orange. If the TV has a comb filter, the lines would not be colored at
> all.

I don't really know anything about NTSC encoding, but... the original 
Rev0 Apple II only displayed 4 colors.  Using the high bit to phase 
shift half a pixel didn't come until later (or as a user mod to the Rev 
0).  There would have been no way to compensate for the color shifts. 
Would this also cause vertical lines to look jagged on a monochrome 
monitor?

All I do know is that the Apple II's NTSC signal completely freaks out 
my InFocus projector.

> I don't have an old apple ][, I just have //e's, so I can't try it on
> my own.
> Does anybody know other reasons for the long cycle?
> 
> Ferdinand Meyer-Hermann

Along theses lines, why didn't the IIe add an interlaced display option? 
  My Apple III does, and it makes for a very nice display, especially 
with  the long persistence phosphor of the Monitor III.  If it would 
have displayed page 1 and page 2 in alternating fields, you could get 
560x384 DHGR graphics.

Dave...
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