SID chip

[Mikko Helin]

>
>> Well, fooling around with 3 VCOs and the filter was probably the trick :)
>
>Nope, they way i've seen numerous C-64 coders (i'm one too, you should
>see what can be done on the C-64 nowadays!) do it, is to
>really fast modify the volume, like the way you play samples through a
>PC-Speaker (believe me, I KNOW!)
Yes, if you are going to use it as a sample player, but the SID indeed
has 3 DCOs and one VCF, which state-variable type with three multiplying
12 bit DACs used as digitally controlled resistors (FC Q). Oscillator
can even sync to each other (two oscs). The third DCO is mainly for
EG functions, as there are no EGs, why CPU is needed to control
DCOs, VCFs and VCA. There's some noise generator, too.

SID can be accessed thru some registers, it could be used alone thru PC's
printer port with some additional logic like an eight-bit buffer/latch
and an 1 Mhz oscillator. SID has 5 address lines (thats what for the
latch is needed) and an eight bit data bus, OSC input and chip
select + data read/write lines, too. I wish somebody carried out
that idea of interfacing SID thru printer port.

-Mikko