S-SMP

The SPC700 is the CPU portion of the S-SMP processor used to run the sound and music of the SNES. It is an 8-bit CPU with capabilities similar to the 6502.

Memory Layout

TODO

Registers

TODO

DSP Registers

A DSP register can be selected with $F2, after which it can be read or written via $FE. Often it is useful to load the register address into A, and the value to send in Y, so that ***MOV $F2, AY*** can be used to do both in one 16-bit instruction.

Voices

There are 8 voices, numbered 0 to 7. Each voice X has 10 registers in the range $X0-$X9.

Name	Address	Bits	Notes
VOL (L)	$X0	SVVV VVVV	Left channel volume, signed.
VOL (R)	$X1	SVVV VVVV	Right channel volume, signed.
P (L)	$X2	LLLL LLLL	Low 8 bits of sample pitch.
P (H)	$X3	xxHH HHHH	High 6 bits of sample pitch.
SCRN	$X4	SSSS SSSS	Selects a sample source entry from the directory (see DIR below).
ADSR (1)	$X5	EDDD AAAA	ADRS enable (E), decay rate (D), attack rate (A).
ADSR (2)	$X6	LLLR RRRR	Sustain level (L), sustain rate (R).
GAIN	$X7	0VVV VVVV 1MMV VVVV	Mode (M), value (V).
ENVX	$X8	0VVV VVVV	Reads current 7-bit value of ADSR/GAIN envelope.
OUTX	$X9	SVVV VVVV	Reads signed 8-bit value of current sample wave multiplied by ENVX, before applying VOL.

ADSR

This controls an Attack-Decay-Sustain-Release envelope that automatically adjusts the sample's envelope volume (ENVX) over time.

• ***E***: 1 to enable ADSR envelope, otherwise uses GAIN directly.
• ***A***: Attack speed. $F for instant.
• ***D***: Decay speed, time to decay from full volume to the sustain level after the initial attack.
• ***L***: Sustain level.
• ***R***: Sustain release, speed of decay to 0 after note off.

GAIN

This register has 5 modes:

• 0VVV VVVV sets ENVX directly.
• 110V VVVV Linear slide up to 100% volume with rate V.
• 111V VVVV Bent-line (fast to 75%, then slower to 100%) slide up with rate V.
• 100V VVVV Linear slide down to 0% volume with rate V.
• 101V VVVV Exponential slide down to 0% volume with rate V.

Instruction Set

Official instruction names and syntax for SPC-700 instruction were provided by Sony. However, because of its architectural similarity to 6502, some prefer to rename and remap them using a 6502 style syntax. Both are provided here.

SPC-700 Instruction Set

Instruction	6502-Style	Opcode	Bytes	Cycles	Flags	Notes
TODO

IPL Boot ROM

TODO

BRR Samples

TODO (See Links section below.)

See Also

• Booting the SPC700 - Guide for setting up the SPC program after reset.
• Tools - Lists tools for building SPC700 code.
• APU pinout - Chip pinouts.

Links

• SPC 700 Documentation - Article by Gau.
• SPC700 Reference - Superfamicom.org wiki article.
• Bit Rate Reduction - Superfamicom.org wiki article, documents BRR sample format.
• SNES APU DSP BRR Samples - Fullsnes documentation of BRR sample format.