Rubywand <rubywand@swbell.net> wrote:

>      As to why the original CDA might want to write to $00/C05D, I don't
> know.

The Zip Chip (and Zip GS) use the annunciator locations ($C058 to $C05F)
to access the on-chip registers.  There is a special sequence to enable
and disable access to the Zip registers, so that normal use of the
annunciators still works.

For the Zip GS, writing to $C05D sets the CPU speed (a 4 bit field, with
sixteen settings ranging from 6.25% to 100%).

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