Pokémon mini Development Documentation

SUB = Subtraction (8-bits)

Hex	Mnemonic	Cycles
10	SUB A,A	2
11	SUB A,B	2
12 nn	SUB A,#nn	2
13	SUB A,[HL]	2
14 ll	SUB A,[BR:ll]	3
15 ll hh	SUB A,[hhll]]]	4
16	SUB A,[IX]	2
17	SUB A,[IY]	2
CE 10 dd	SUB A,[IX+dd]	4
CE 11 dd	SUB A,[IY+dd]	4
CE 12	SUB A,[IX+L]	4
CE 13	SUB A,[IY+L]	4
CE 14	SUB [HL],A	4
CE 15 nn	SUB [HL],#nn	5
CE 16	SUB [HL],[IX]	5
CE 17	SUB [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))

; SUB Ds, Sc
;
; Ds = Destination
; Sc = Source

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

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

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

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

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

Description

Subtracts 8-bits Source from 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 exceeds 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
SUB A, $80
; A = 0xD5 (0x55 - 0x80 = 0x(1)D5)
; SC = (Zero=0):(Carry=0):(Overflow=1):(Negative=1)

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

; ( Decimal = 1, Unpack = 0 )
; A = 0x10
SUB A,``
``$01
; A = 0x09 (10 - 01 = 09)
; 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)
SUB A, $01
; A = 0x0E (0xF - 0x1 = 0x(0)E)
; SC = (Zero=0):(Carry=0):(Overflow=0):(Negative=0)

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