C64-dev/reference/sid-registers.md

SID 6581 Register Map — Quick Reference

SID base address: $D400 (54272) All registers write-only except $D419–$D41C.

Voice Registers

Offset	Addr	Dec	Voice	Name	Description
+0	$D400	54272	1	FRELO1	Freq low
+1	$D401	54273	1	FREHI1	Freq high
+2	$D402	54274	1	PWLO1	Pulse width low
+3	$D403	54275	1	PWHI1	Pulse width high (bits 3-0)
+4	$D404	54276	1	VCREG1	Control register
+5	$D405	54277	1	ATDCY1	Attack/Decay
+6	$D406	54278	1	SUREL1	Sustain/Release
+7	$D407	54279	2	FRELO2	Freq low
+8	$D408	54280	2	FREHI2	Freq high
+9	$D409	54281	2	PWLO2	Pulse width low
+A	$D40A	54282	2	PWHI2	Pulse width high
+B	$D40B	54283	2	VCREG2	Control register
+C	$D40C	54284	2	ATDCY2	Attack/Decay
+D	$D40D	54285	2	SUREL2	Sustain/Release
+E	$D40E	54286	3	FRELO3	Freq low
+F	$D40F	54287	3	FREHI3	Freq high
+10	$D410	54288	3	PWLO3	Pulse width low
+11	$D411	54289	3	PWHI3	Pulse width high
+12	$D412	54290	3	VCREG3	Control register
+13	$D413	54291	3	ATDCY3	Attack/Decay
+14	$D414	54292	3	SUREL3	Sustain/Release

Filter and Global Registers

Offset	Addr	Dec	Name	Description
+15	$D415	54293	SIGVOL	Filter cutoff freq low (bits 2-0)
+16	$D416	54294	FRESHI	Filter cutoff freq high byte
+17	$D417	54295	RESON	Resonance (7-4) / filter routing (2-0)
+18	$D418	54296	SIGVOL	Filter mode (7-4) / volume (3-0)
+19	$D419	54297	POTX	Paddle X (READ-ONLY)
+1A	$D41A	54298	POTY	Paddle Y (READ-ONLY)
+1B	$D41B	54299	RANDOM	Voice 3 oscillator (READ-ONLY, random)
+1C	$D41C	54300	ENV3	Voice 3 envelope (READ-ONLY)

Control Register Bits (VCREG)

Bit	Name	Description
7	NOISE	Noise waveform
6	PULSE	Pulse waveform
5	SAW	Sawtooth waveform
4	TRI	Triangle waveform
3	TEST	Test bit (disables osc)
2	RING	Ring modulation
1	SYNC	Sync to previous voice
0	GATE	1=start AD, 0=start Release

ATDCY (Attack/Decay)

Bits	Range	Description
7-4	0-15	Attack rate
3-0	0-15	Decay rate

SUREL (Sustain/Release)

Bits	Range	Description
7-4	0-15	Sustain level (15=max)
3-0	0-15	Release rate

Filter Mode Register ($D418) Bits

Bit	Name	Description
7	3OFF	Disconnect voice 3 from output
6	HP	High-pass filter
5	BP	Band-pass filter
4	LP	Low-pass filter
3-0	VOL	Master volume (0-15)

Frequency Formula

Register = (Hz × 16777216) / ClockHz
NTSC: ClockHz = 1,022,730   Register = Hz / 0.0609594
PAL:  ClockHz = 985,248     Register = Hz / 0.0587721

Note Frequencies (NTSC hex register values)

Note	Freq	Hex		Note	Freq	Hex
C3	130.8	$086C		C4	261.6	$10D9
D3	146.8	$0975		D4	293.7	$12EA
E3	164.8	$0A9B		E4	329.6	$1537
F3	174.6	$0B40		F4	349.2	$1680
G3	196.0	$0C91		G4	392.0	$1921
A3	220.0	$0E16		A4	440.0	$1CCC
B3	246.9	$0F9C		B4	493.9	$1F38
C5	523.3	$21B3		C6	1046.5	$4366