ARM2SID IO connection with diodes:
The ARM2SID IO connection with diodes and a pullup resistor (all parts are
provided with ARM2SID with 30 cm cable wires) is necessary only if you
want to use all possibilities of ARM2SID. In case, that you do not want to use
the 2nd SID on an address $DExx, you do not have to connect IO1 and just
connect the ARM2SID IO pin directly to the IO2 of expansion connector for
the SFX Sound Expander $DFxx. If you do not want to use ARM2SID on
address $DExx and $DFxx, you do not have to connect ARM2SID IO pin at all.
$D5xx addresses decoding in Commodore C128
Using $D5xx addresses in C128 is a little bit difficult because the SIDs chip-
select pin in C128 addresses only $D400-$D4FF range, unlike C64 where it is
$D400-$D7FF. You still need to connect the A8 address pin to the CPU, but
you have to somehow extend the address range of the SIDs chip-select. It is
more complicated, you can not extend the range for C128 mode, you can do
it only for C64 mode where the range of $D5xx addresses is usable (free).
