Re: Sound-makes only one click?

[david@uow.edu.au (David Wilson)]

dempson@actrix.gen.nz (David Empson) writes:

>Dave Althoff <dalloff@freenet.columbus.oh.us> wrote:

>> ($C036..Is that right?  I thought I always used $C030...)

>The ][/][+ and IIe don't fully decode the address, so anything from
>$C030 to $C03F will toggle the speaker.  Similarly for cassette out
>($C02x), strobe ($C04x) and paddle trigger ($C07x).

>This is true to a lesser extent for the keyboard buffer ($C00x) and
>strobe ($C01x).  They behave this way on the II+, but the IIe redefines
>all the nonzero locations in each range for mode control and detection.
>The IIe $C001-F locations are write-only, and reading them will still
>access the keyboard buffer.

Actually, the 0 location gets a new use as well. What happens is that
reading C000..C00F remains as on the ][+ while writing to any location
in the same range clears or sets one of 8 flags. Bits 3,2,1 select the
flag while bit 0 is the data written to the flag.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia  david@uow.edu.au