Useful Code Snippets

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Useful code snippets for the 65c816 ASM and general SNES hardware.

65c816 S-CPU

Wait for H-Blank

-
BIT $4212
BVS -
-
BIT $4212
BVC -

Inverse the accumulator (8-bit)

EOR #$FF
INC

Inverse the accumulator (16-bit)

EOR #$FFFF
INC

65c816 SA-1 CPU

Unsigned 16 bit x 16 bit = 32 bit multiplication

by Akaginite

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; 16bit * 16bit Multiplication SA-1 version
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Argusment
; $00-$01 : Multiplicand
; $02-$03 : Multiplier
; Return values
; $04-$07 : Product
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

MathMul16_16:	STZ $2250
		REP #$20
		LDA $00
		STA $2251
		ASL A
		LDA $02
		STA $2253
		BCS +
		LDA.w #$0000
+		BIT $02
		BPL +
		CLC
		ADC $00
+		CLC
		ADC $2308
		STA $06
		LDA $2306
		STA $04
		SEP #$20
		RTS