SUB = Subtraction (8-Bits)

Hex Mnemonic Cycles
10 SUB A, A 8
11 SUB A, B 8
12 nn SUB A, #nn 8
13 SUB A, [HL] 8
14 nn SUB A, [N+#nn] 12
15 nn nn SUB A, [#nnnn]]] 16
16 SUB A, [X] 8
17 SUB A, [Y] 8
CE 10 ss SUB A, [X+#ss] 16
CE 11 ss SUB A, [Y+#ss] 16
CE 12 SUB A, [X+L] 16
CE 13 SUB A, [Y+L] 16
CE 14 SUB [HL], A 16
CE 15 nn SUB [HL], #nn 20
CE 16 SUB [HL], [X] 20
CE 17 SUB [HL], [Y] 20

Execute

#nn     = Immediate unsigned 8-Bits
#ss     = Immediate signed 8-Bits
A       = Register A
B       = Register B
[N+#nn] = Memory: (I shl 16) or (N shl 8) or #nn
[HL]    = Memory: (I shl 16) or HL
[X]     = Memory: (XI shl 16) or X
[Y]     = Memory: (YI shl 16) or Y
[#nnnn] = Memory: (I shl 16) or #nnnn
[X+#ss] = Memory: (XI shl 16) or (X + #ss)
[Y+#ss] = Memory: (YI shl 16) or (Y + #ss)
[X+L]   = Memory: (XI shl 16) or (X + signed(L))
[Y+L]   = Memory: (YI shl 16) or (Y + signed(L))
    
; SUB Ds, Sc
;
; Ds = Destination
; Sc = Source

; (If flags BCD=0 and NIBBLE=0)
Ds = Ds - Sc

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

; (If flags BCD=0 and NIBBLE=1)
Ds & 0x0F = (Ds & 0x0F) - (Sc & 0x0F)

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

; (If flags BCD=1 and NIBBLE=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 BCD=1 and NIBBLE=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

8-Bits Source subtracts to the 8-Bits Destination.

Conditions

If flags BCD=0 and NIBBLE=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)

Sign: Set when bit 7 of the result is 1

If flags BCD=0 and NIBBLE=1

Zero: Set when result is 0

Carry: Set when result is < 0

Overflow: Set when result overflow 4-bits signed range (< -16 OR > 15)

Sign: Set when bit 3 of the result is 1

If flags BCD=1 and NIBBLE=0

Zero: Set when result is 0

Carry: Set when result is < 0

Overflow: Always Reset

Sign: Always Reset

If flags BCD=1 and NIBBLE=1

Zero: Set when result is 0

Carry: Set when result is < 0

Overflow: Always Reset

Sign: Always Reset

Examples

; A = 0x55
SUB A, $80
; A = 0xD5 (0x55 - 0x80 = 0x(1)D5)
; F = (Zero=0):(Carry=0):(Overflow=1):(Sign=1)
    
; B = 0x31
; A = 0xCF
SUB A, B
; B = 0x31
; A = 0x9E (0xCF - 0x31 = 0x(0)9E)
; F = (Zero=0):(Carry=0):(Overflow=0):(Sign=0)
    
; ( BCD = 1, NIBBLE = 0 )
; A = 0x10
SUB A, $01
; A = 0x09 (10 - 01 = 09)
; F = (Zero=0):(Carry=0):(Overflow=0):(Sign=0)
    
; ( BCD = 0, NIBBLE = 1 )
; A = 0x3F (Note, in "nibble mode" the high nibble is always discarded)
SUB A, $01
; A = 0x0E (0xF - 0x1 = 0x(0)E)
; F = (Zero=0):(Carry=0):(Overflow=0):(Sign=0)
    

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