From leitner@cs.odu.eduFri Jul 28 15:23:06 1995
Date: Sun, 23 Jul 1995 17:06:20 -0400 (EDT)
From: Larry Leitner <leitner@cs.odu.edu>
To: LX Rudis <lx@fht.com>
Cc: analogue heaven <analogue@hyperreal.com>
Subject: Re: C64 software / SID Chip

For all thos interested...

I recently found a programmer's guide with the SID chip description.

 
(voice1)

($D400-D401) Frequency is controlled by 2 8bit frequency registers.

($D402-D403) Pulsewidth is controlled by another two bytes 
             (only 12 bits used)

($D404) Waveform/Gate is controlled by one byte.
	bit 0 - gate bit, which turns voice on/off
	bit 1 - sychronization (with voice 3 if selected)
	bit 2 - ring modulation (with voice 3 if selected)
	bit 3 - test bit (when set to 1 it disables voice)
	bit 4,5,6,7  selects waveforms

Envelope
($D405) high nibble/low nibble - controls Attack/Decay
($D406) high nibble/low nibble - controls Sustain/Release

$(D407-D40D) Voice 2 - everything is the same as voice 1 above except 
	that if sync or ring mod are used voice 1 mods voice 2

$(D40E-D414) Voice 3 - everything is the same as Voice 1/2 except that if
	 ring mod or sync are selected, voice 2 mods voice 3

($D415-D416) Filter Cutoff Frequency - first 11 bits used

($D417) Filter Control - high nibble controls resonance, bits 0,1,2 
	contol which voice go to the filter.  When bit 3 is set you can filter an 
	external source.  It doesn't say where you put this source.  

($D418) Volume and Filter Type - low nible sets volume for entire chip
	Bits 4,5,6 set lowpass, bandpass, highpass 
	(you can do more than one at a time)
        bit 7 disables the output of voice 3, so you can use it as a 
	modulator.

($D419-D41A) Paddle Inputs (PONG!) - just what every voice chip needs.  
	Actually these are A/D converters, input range 0-5 volts, 
	register range 255-0 

($D41B) Number generator - apparently the VCO/DCO(?) output is mirrored 
	here and can be used as a number generator with values of 0-255

($D41C) Envelope out - when voice 3 output is turned off this register 
	holds the value of the envelope 0-255

Not bad for $16.50 from JameCo.  Of course all of these registers are 
mapped in the C64/128.  I couldn't tell you about the actual pinouts.

Larry 

 ========================================================================
 = Larry Leitner leitner@cs.odu.edu WODU AM640 Techno, Trance, Ambient  +
 ========================================================================

 (Roland A-Juno-2 Manual)
 VCF Resonance:
 As you increase the value, the created sound will become more unusual,
 more electronic in nature.