Re: PAL Apple IIe (was Re: Apple III?)

[dempson@actrix.gen.nz (David Empson)]

David Wilson <david@uow.edu.au> wrote:

> pim@planet.nl (Pim Blokland) writes:
> >In article <1e3bdvl.1fvnha2ip2lc0N%dempson@actrix.gen.nz>,
> >dempson@actrix.gen.nz (David Empson) wrote:
> 
> >> The PAL IIe runs at a slightly lower clock frequency than the NTSC IIe,
> 
> >Is that so? I never knew that! I've owned an UK //e for years (made in
> >Ireland), and I always assumed the speed was 1.023 MHz, just like the USA
> >models. What exactly are the speeds?
> 
> The same applies to a EuroPlus. The 14.31818 MHz main xtal is replaced by one
> that increases the horizontal timing to 64us (15625Hz). Unfortunately I cannot
> read the number off my //e xtal so I will have to try and calculate it:
> 
> NTSC  14318180 / 14 / 65 = 15734 Hz
> PAL   15625 * 14 * 65 = 14218750

To completely answer the original question: the CPU is running at one
fourteenth of the master clock speed, thus 1.015625 MHz for a PAL model,
or 1.0227... MHz for an NTSC model.

With the NTSC model there is the added timing glitch of every 65th CPU
cycle being stretched so that it is 8/7 of the normal duration.  (This
is required to correct the NTSC video timing.)  I'm pretty sure this is
not required in a PAL model.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand