Re: 6809 / 6702 puzzle

On Sat 21 Apr 2012 at 14:55:00 +0200, davee.roberts@fsmail.net wrote:
> My understanding therefore is that the 6702 is addressed when the
> address lines are 1110 1111 1110 00XX or $EFE0 through $EFE3.

As it turns out, *both* the notions of $EFE0 through $EFE3 and 
"E F xxx0 xxxx", as found on the schematic, are valid.

The bigger range selects "something", which makes that the value as you
read it back isn't that of unconnected address space. On the PET,
unconnected address space reads back as the high byte of its address.

Inside this range, only $EFE0 through $EFE3 actually read the 6702
output. Other addresses return $FF (rather than $EF).

Waterloo microMonitor

>d ef80.80
;ef80 ff ff ff ff ff ff ff ff *........
;ef88 ff ff ff ff ff ff ff ff *........
;ef90 ef ef ef ef ef ef ef ef *........
;ef98 ef ef ef ef ef ef ef ef *........
;efa0 ff ff ff ff ff ff ff ff *........
;efa8 ff ff ff ff ff ff ff ff *........
;efb0 ef ef ef ef ef ef ef ef *........
;efb8 ef ef ef ef ef ef ef ef *........
;efc0 ff ff ff ff ff ff ff ff *........
;efc8 ff ff ff ff ff ff ff ff *........
;efd0 ef ef ef ef ef ef ef ef *........
;efd8 ef ef ef ef ef ef ef ef *........
;efe0 d6 d6 d6 d6 ff ff ff ff *........
;efe8 ff ff ff ff ff ff ff ff *........
;eff0 00 50 6b 3a ef ef ef ef *.Pk:....
;eff8 ef ef ef ef ef ef ef ef *........
;f000 10 ce 02 20 bd fe 74 bd *... ..t.
>
>d ef00.80
;ef00 ff ff ff ff ff ff ff ff *........
;ef08 ff ff ff ff ff ff ff ff *........
;ef10 ef ef ef ef ef ef ef ef *........
;ef18 ef ef ef ef ef ef ef ef *........
;ef20 ff ff ff ff ff ff ff ff *........
;ef28 ff ff ff ff ff ff ff ff *........
;ef30 ef ef ef ef ef ef ef ef *........
;ef38 ef ef ef ef ef ef ef ef *........
;ef40 ff ff ff ff ff ff ff ff *........
;ef48 ff ff ff ff ff ff ff ff *........
;ef50 ef ef ef ef ef ef ef ef *........
;ef58 ef ef ef ef ef ef ef ef *........
;ef60 ff ff ff ff ff ff ff ff *........
;ef68 ff ff ff ff ff ff ff ff *........
;ef70 ef ef ef ef ef ef ef ef *........
;ef78 ef ef ef ef ef ef ef ef *........
;ef80 ff ff ff ff ff ff ff ff *........
>

(cut & pasted from VICE, but of course I double-checked this before I
put this in VICE :-)

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert  -- There's no point being grown-up if you 
\X/ rhialto/at/xs4all.nl    -- can't be childish sometimes. -The 4th Doctor

       Message was sent through the cbm-hackers mailing list