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ORA
When (T) = 0, (A) ← (A) ∨ (M)
Op e r a t io n :
F u n c t io n :
When T = 0, this instruction transfers the contents of A and M
to the ALU which performs a bit-wise "OR", and stores the
result in A.
When T = 1, this instruction transfers the contents of M(X) and
the M to the ALU which performs a bit-wise OR, and stores the
result in M(X). The contents of A remain unchanged, but status
flags are changed.
M(X) represents the contents of memory where is indicated by
X.
St a t u s fla g :
N :
V :
T :
B :
I :
D :
Z :
C :
Addressing mode
∆ORA∆#$nn
Immediate
∆ORA∆$zz
Zero page
∆ORA∆$zz,X
Zero page X
∆ORA∆$hhll
Absolute
∆ORA∆$hhll,X
Absolute X
∆ORA∆$hhll,Y
Absolute Y
∆ORA∆($zz,X)
(Indirect X)
∆ORA∆($zz),Y
(Indirect Y)
Note: When T=1, add 3 to the cycle number.
74
OR
MEMORY WITH
(T) = 1, (M(X)) ← (M(X)) ∨ (M)
N is when bit 7 is 1 after the operation; otherwise N is 0.
No change
No change
No change
No change
No change
Z is 1 when the execution result is 0; otherwise Z is 0.
No change
Statement
A
CCUMULATOR
Byte number
Machine codes
09
, nn
16
16
05
, zz
16
16
15
, zz
16
16
0D
, ll
, hh
16
16
16
1D
, ll
, hh
16
16
16
19
, ll
, hh
16
16
16
01
, zz
16
16
11
, zz
16
16
ORA
Cycle number
2
2
2
3
2
4
3
4
3
5
3
5
2
6
2
6
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