[Coco] Coco3 question

[Joef6809]

Ahhh Thats it, I was assuming 60Hz but it should have been 59.923.
It was driving me crazy why boink wouldn't work anymore.
At 60Hz it was "thining" the Cycles per second to much.

----- Original Message ----- 
From: <jdaggett at gate.net>
To: "Joe F" <joef6809 at gmail.com>; "CoCoList for Color Computer Enthusiasts" 
<coco at maltedmedia.com>
Sent: Tuesday, February 12, 2008 10:38 PM
Subject: Re: [Coco] Coco3 question


> On 12 Feb 2008 at 17:14, Joe F wrote:
>
>> Does anyone know if the coco3 has 262 or 263 scan lines.
>> the 6847 spec sheet indicates 262.5 but I'm not sure it applies to the
>> GIME as well. thanks.
>
> The GIME appears to have 262 lines per frame. it is progressive scan not 
> interlaced
> scanned. This is based on the specifications for the RGB monitor and some 
> simple math.
>
> Take the xtal frequency of the GIME and divide it by 1824 and you get 
> 16699.76 Hz. Now
> divide that by 262 and you get 59.923 Hz. The CM8 specs are 15700 +/- 100 
> Hz for the
> horizontal frequency and 59.96 Hz. for the vertical frequency. The 
> horizontal line frequency
> is a multiple of the vertical frame rate. Has to be. SInce timing is 
> genreated from the main
> xtal, integer dividers are far more easier to make than a fractional 
> dividers unless you use a
> phase acummalator to act as a divider. That becomes a bit more complex 
> than a simple
> integer divider.
>
> This is the best combination of dividers that allows the GIME chip to meet 
> the CM8
> specifications which was designed for the COCO3.
>
> james