[Coco] PAL Coco 1/2 schematics/timings

[Mark McDougall]

On 10/09/2010 4:40 PM, Ciaran Anscomb wrote:


> As the PAL and NTSC line rates are nearly identical, the main clock

> stays the same (actually *some* Dragons *slightly* alter this to

> 14.218MHz, but not all).  Extra circuitry (including another crystal) is,

> however, added to encode the colour information.

>

> PAL has 50 more lines per field, so some simple logic is included that

> stops the clock to the VDG at two points during every field and inserts

> 25 "fake" blank scanlines.



> Of course, PAL CoCos may well do things in a subtly different way (which

> would explain a lot...), but I've no schematic to prove that so if

> anyone can come up with something, I'd be just as interested!


Bob Devries was kind enough to send me a scan of the video portion of the 
Coco 2 manual. And yes, this is exactly what the Coco 2 does as well!

Interesting, as I assumed that the PAL Coco used a different base clock. But 
as it turns out, this makes things a lot easier for me! ;)

Regards,

-- 

|              Mark McDougall                | "Electrical Engineers do it

|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"