[Coco] 384 or 450 scanlines ?

[Arthur Flexser]

Gene, I think you're confusing the 6847Y with the lowercase-capable 6847T1.

Art

On Mon, Jan 13, 2014 at 2:54 PM, Gene Heskett <gheskett at wdtv.com> wrote:
> On Monday 13 January 2014 14:47:33 Arthur Flexser did opine:
>
>> I guess what's puzzling me is this:  as I now understand it, every
>> frame is ordinarily repeated twice in succession identically, with the
>> second repetition landing smack on top of the first, with a frame
>> occurring every 60th of a second and using only every other scan line.
>>  Wouldn't it have looked better if the second repetition was one scan
>> line offset from the first instead of on top of it?  Would the 6947Y
>> VDG accomplish that?
>>
>> Art
>
> No, and to my knowledge it can't.  The Y version could only do both lower
> case and upper case, which has nothing to do with this.  To all, generating
> an interlaced signal for the sync's involves a huge number of binary
> divider stages, every one of with is working with odd numbers made even by
> doubling the parent clocking.  TV sync generators of the day were often
> done in ttl logic, needing quite a few chips (10 or more) to get the job
> done.  Thats chip real estate that did not exist when even the coco3 was
> being designed.
>
> Such chips have been designed in the later '90's, but even then they needed
> lots of external supervision to get their ducks all waddling in a row.
>
>> On Mon, Jan 13, 2014 at 1:48 PM, Nick Marentes <nickma at optusnet.com.au>
> wrote:
>> > Arthur Flexser <flexser at ...> writes:
>> >> Thanks for the explanation, John.  I'm curious, though, about why the
>> >> 6847 non-interlaced VDG was chosen for the CoCo rather than the 6847Y
>> >> interlaced version.  And, would a 6847Y VDG work if you replaced the
>> >> 6847 in a CoCo with it?
>> >
>> > And I thought that the interlacing was fixed in the TV/monitor of an
>> > interlaced set. That a monitor always provides 525 lines interlaced
>> > (NTSC).
>> >
>> > That's why I thought the CoCo had to provide either 2 fields or 1
>> > field and a blank field to satisfy the interlaced function of the
>> > monitor.
>> >
>> > I guess it makes sense that the early video game systems and TV's
>> > would just create a single 262 line display that is repeated. I
>> > didn't know that the TV/monitor could stop creating the interlaced
>> > field.
>> >
>> > Nick
>> >
>> >
>> >
>> >
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>
> Cheers, Gene
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