SPC-700 instruction set

The Sony SPC-700 CPU is part of the S-SMP sound processor of the SNES. It runs at 2.048 MHz, and behaves similarly to a 6502 at 1.024 MHz with some extensions.

Architecture

The SPC-700 has a 16-bit address space, and a similar set of registers to the 6502.

Registers

• A - 8-bit accumulator
• X - 8-bit index
• Y - 8-bit index
• YA - 16-bit pair of A (lsb) and Y (msb).
• PC - program counter
• SP - stack pointer
• PSW - program status word: NVPBHIZC
  • N - negative flag (high bit of result was set)
  • V - overflow flag (signed overflow indication)
  • P - direct page flag (moves the direct page to $0100 if set)
  • H - half carry flag (carry between low and high nibble)
  • I - interrupt disable (unused: the S-SMP has no attached interrupts)
  • Z - zero flag (set if last result was zero)
  • C - carry flag

Differences from the 6502:

• A 16-bit combined YA register is available for some operations.
• The direct page can be moved to $0100. (Rarely used.)
• A half carry flag that is useful for nibble operations.
• No decimal mode.

Addressing Modes

• imm - 8-bit immediate value
• dp - 8-bit direct page offset ($0000+dp or $01000+dp)
• !abs - 16-bit absolute address
• rel - relative offset in two's complement
• (i) - direct-page relative index (P * $100 + i)
• (i)+ - direct-page relative index with post-increment (i is incremented after read)
• [addr]+i - indirect indexed (add index after lookup)
• [addr+i] - indexed indirect (add index before lookup)

Instructions

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.

Sony instruction convention puts the destination on the left, source on the right (Intel syntax).

Cycles in this table are 1.024 MHz CPU cycles. Each one is equal to 2 clocks of the 2.048 Mhz S-SMP.

SPC-700 Instruction Set

Instruction	6502-Style	Opcode	Bytes	Cycles	Flags	Notes
8-bit move memory to register
MOV A, #imm	LDA #imm	E8	2	2	N......Z
MOV A, (X)	?	E6	1	3	N......Z
MOV A, (X)+	?	BF	1	4	N......Z	X++ after read
MOV A, dp	LDA zp	E4	2	3	N......Z
MOV A, dp+X	LDA zp, X	F4	2	4	N......Z
MOV A, !abs	LDA abs	E5	3	4	N......Z
MOV A, !abs+X	LDA abs, X	F5	3	5	N......Z
MOV A, !abs+Y	LDA abs, Y	F6	3	5	N......Z
MOV A, [dp+X]	LDA (zp, X)	E7	2	6	N......Z
MOV A, [dp]+Y	LDA (dp), Y	F7	2	6	N......Z
MOV X, #imm	LDX #imm	CD	2	2	N......Z
MOV X, dp	LDX zp	F8	2	3	N......Z
MOV X, dp+Y	LDX zp, Y	F9	2	4	N......Z
MOV X, !abs	LDX abs	E9	3	4	N......Z
MOV Y, #imm	LDY #imm	8D	2	2	N......Z
MOV Y, dp	LDY zp	EB	2	3	N......Z
MOV Y, dp+X	LDY zp, X	FB	2	4	N......Z
MOV Y, !abs	LDY abs	EC	3	4	N......Z
8-bit move register to memory
MOV (X), A	?	C6	1	4	........
MOV (X)+, A	?	AF	1	4	........	X++ after read
MOV dp, A	STA zp	C4	2	4	........
MOV dp+X, A	STA zp, X	D4	2	5	........
MOV !abs, A	STA abs	C5	3	5	........
MOV !abs+X, A	STA abs, X	D5	3	6	........
MOV !abs+Y, A	STA abs, Y	D6	3	6	........
MOV [dp+X], A	STA (zp, X)	C7	2	7	........
MOV [dp]+Y, A	STA (zp), Y	D7	2	7	........
MOV dp, X	STX zp	D8	2	4	........
MOV dp+Y, X	STX zp, Y	D9	2	5	........
MOV !abs, X	STX abs	C9	3	5	........
MOV dp, Y	STY zp	CB	2	4	........
MOV dp+X, Y	STY zp, X	DB	2	5	........
MOV !abs, Y	STY abs	CC	3	5	........
8-bit move register to register / special direct page moves
MOV A, X	TXA	7D	1	2	N......Z
MOV A, Y	TYA	DD	1	2	N......Z
MOV X, A	TAX	5D	1	2	N......Z
MOV Y, A	TAY	FD	1	2	N......Z
MOV X, SP	TSX	9D	1	2	N......Z
MOV SP, X	TXS	BD	1	2	........
MOV dp, dp	?	FA	3	5	........
MOV dp, #imm	?	8F	3	5	........
TODO

Links

• SPC700 Reference - CPU Instruction Set at superfamicom.org wiki