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D EC
(A) ← (A) – 1, or
Op e r a t io n :
(M) ← (M) – 1
F u n c t io n :
This instruction subtracts 1 from the contents of A or M.
St a t u s fla g :
N :
V :
T :
B :
I :
D :
Z :
C :
Addressing mode
∆DEC∆A
Accumulator
∆DEC∆$zz
Zero page
∆DEC∆$zz,X
Zero page X
∆DEC∆$hhll
Absolute
∆DEC∆$hhll,X
Absolute X
DEC
REMENT BY ONE
N is 1 when bit 7 is 1 after the addition; otherwise N is 0.
No change
No change
No change
No change
No change
Z is 1 when the operation result is 0; otherwise Z is 0.
No change
Statement
Machine codes
Byte number
1A
16
C6
, zz
16
16
D6
, zz
16
16
CE
, ll
, hh
16
16
16
DE
, ll
, hh
16
16
16
D EC
Cycle number
1
2
2
5
2
6
3
6
3
7
57
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