[Coco] Coco3 question

[Arthur Flexser]

Whether it is 262 or 262.5 does affect the nominally correct value for the time
between horizontal sync interrupts.  Is that why you're concerned with this
question?  I'm pretty sure that the typical extent of small timing differences
between one CoCo and another is greater than the percentage difference between
262 and 262.5, so the distinction is a bit academic.  At one point, I compared a
few CoCo 2s, and found they differed from one another by a few tenths of a
percent.  I believe there was an adjustable capacitor you could use to fine tune
this, though I never played around with it.  (I used the CoCo in an experimental
psychology laboratory to measure reaction times to verbal stimuli placed on
screen, so I was curious as to how much variation I had between the half-dozen
or so CoCo's I was using.  Since I used a count of HS interrupts, which are
about 1/16 millisecond apart, the CoCo was very accurate for this purpose.)

Flexser, A.J. (1988)  Accurate display timing using an enhanced Basic for the
Tandy Color Computer.  	Behavior Research Methods, Instruments, and Computers,
19, 457-459.

Art

On Tue, 12 Feb 2008, Joef6809 wrote:

> yes that makes sense. so the 6847 is 262 lines and I guess the coco3 would 
> be the same?
> ----- Original Message ----- 
> From: "Mike Pepe" <lamune at doki-doki.net>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Tuesday, February 12, 2008 7:27 PM
> Subject: Re: [Coco] Coco3 question
> 
> 
> > Joef6809 wrote:
> >> Didn't say it made sense, I'm just saying thats what the 6847 sheet says.
> >> Page 11 of the MC6847 or page 12 of the MC6847T1 sheet clearly states 
> >> that each each frame is 262.5 Interlaced and 262 non-interlaced line. 
> >> Unless I'm reading it wrong.
> >> Theres a link to it here if you care to wander down this path with me.
> >> http://vcc6809.bravehost.com/techdocs/MC6847.pdf
> >
> > The 6847 version used in the CoCo does not use interlaced sync.
> >
> > I'd guess the "half line" of the 6847Y is one-half of one complete 
> > interlaced line.
> >
> >
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> 
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