Pokémon mini Development Documentation

SBC = Subtraction with Carry (8-bits)

Hex	Mnemonic	Cycles
18	SBC A,A	2
19	SBC A,B	2
1A nn	SBC A,#nn	2
1B	SBC A,[HL]	2
1C ll	SBC A,[BR:ll]	3
1D ll hh	SBC A,[hhll]	4
1E	SBC A,[IX]	2
1F	SBC A,[IY]	2
CE 18 dd	SBC A,[IX+dd]	4
CE 19 dd	SBC A,[IY+dd]	4
CE 1A	SBC A,[IX+L]	4
CE 1B	SBC A,[IY+L]	4
CE 1C	SBC [HL],A	4
CE 1D nn	SBC [HL],#nn	5
CE 1E	SBC [HL],[IX]	5
CE 1F	SBC [HL],[IY]	5

Execute

#nn     = Immediate unsigned 8-bits
dd      = Immediate signed 8-bits
A       = Register A
B       = Register B
[BR:ll] = Memory: (EP shl 16) or (BR shl 8) or #nn
[HL]    = Memory: (EP shl 16) or HL
[IX]    = Memory: (XP shl 16) or IX
[IY]    = Memory: (YP shl 16) or IY
[hhll]  = Memory: (EP shl 16) or hhll
[IX+dd] = Memory: (XP shl 16) or (IX + dd)
[IY+dd] = Memory: (YP shl 16) or (IY + dd)
[IX+L]  = Memory: (XP shl 16) or (IX + signed(L))
[IY+L]  = Memory: (YP shl 16) or (IY + signed(L))

; SBC Ds, Sc
;
; Ds = Destination
; Sc = Source

; (If flags D=0 and U=0)
Ds = Ds - Sc - Carry

;------------------------------------------------

; (If flags D=0 and U=1)
Ds & 0x0F = (Ds & 0x0F) - (Sc & 0x0F) - Carry

;------------------------------------------------

; (If flags D=1 and U=0)
IF (((Ds & 15) - (Sc & 15) - Carry) >= 10) THEN    ; Note: Should be an unsigned check
  Ds = Ds - Sc - Carry - 6
ELSE
  Ds = Ds - Sc - Carry
ENDIF
IF (Ds >= 0xA0) Ds = Ds - 0x60
; NOTE: This isn't accurate, there's some weird effect on a strange condition

;------------------------------------------------

; (If flags D=1 and U=1)
IF (((Ds & 15) - (Sc & 15) - Carry) >= 10) THEN    ; Note: Should be an unsigned check
  Ds & 0x0F = (Ds & 0x0F) - (Sc & 0x0F) - Carry - 6
ELSE
  Ds & 0x0F = (Ds & 0x0F) - (Sc & 0x0F) - Carry
ENDIF

Description

8-bits Source and Carry subtracts to the 8-bits Destination.

Conditions

If flags D=0 and U=0

Zero: Set when result is 0
Carry: Set when result is < 0
Overflow: Set when result overflow 8-bits signed range (< -128 OR > 127)
Negative: Set when bit 7 of the result is 1

If flags D=0 and U=1

Zero: Set when result is 0
Carry: Set when result is < 0
Overflow: Set when result exceeds 4-bits signed range (< -16 OR > 15)
Negative: Set when bit 3 of the result is 1

If flags D=1 and U=0

Zero: Set when result is 0
Carry: Set when result is < 0
Overflow: Always reset
Negative: Always reset

If flags D=1 and U=1

Zero: Set when result is 0
Carry: Set when result is < 0
Overflow: Always reset
Negative: Always reset

Examples

; A = 0x55
; SC = (Carry=1)
SBC A, $80
; A = 0xD4 (0x55 - 0x80 - 0x01 = 0x(1)D4)
; SC = (Zero=0):(Carry=0):(Overflow=1):(Negative=1)

; B = 0x31
; A = 0xCF
; SC = (Carry=0)
SBC A, B
; B = 0x31
; A = 0x9E (0xCF - 0x31 - 0x00 = 0x(0)9E)
; SC = (Zero=0):(Carry=0):(Overflow=0):(Negative=0)

; ( Decimal = 1, Unpack = 0 )
; A = 0x10
; SC = (Carry=1)
SBC A,``
``$01
; A = 0x08 (10 - 01 - 01 = 08)
; SC = (Zero=0):(Carry=0):(Overflow=0):(Negative=0)

; ( Decimal = 0, Unpack = 1 )
; A = 0x3F (Note, in "unpack mode" the high nibble is always discarded)
; SC = (Carry=1)
SBC A, $01
; A = 0x0D (0xF - 0x1 - 0x1 = 0x(0)D)
; SC = (Zero=0):(Carry=0):(Overflow=0):(Negative=0)

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