18
IN STRUC TION S
In d ir e c t Y
Ad d r e s s in g m o d e :
F u n c tio n :
In s tr u c tio n s :
Ex a m p le :
Indirect Y
Specifies the contents in a memory location as the
data for the instruction. The address in the memory
location is determined by the following:
(a) The Operand is used the low-order byte of an
address in the Zero Page memory location and
00
16
of the high-order byte.
(b) The contents of the address in the Zero Page
memory location is used as the low-order byte of
an address. The next Zero Page memory location
is used as the high-order byte.
(c) The Index Register Y is added to the address in
Step b. The result of this addition is the address
in the memory location.
ADC, AND, CMP, EOR, LDA, ORA, SBC, STA
Mnemonic
Machine code
∆
ADC
∆
($1E),Y
71
16
1E
16
Addressing mode
AAAAAA
AAAAAA
AAAAAA
AAAAAA
AAAAAA
AAAAAA
AAAAAA
AAAAAA
(A)
←
(A) + (C) + XX
16
Data (XX
16
)
12E7
16
Op-code (71
16
)
Operand (1E
16
)
1E
16
00
16
FF
16
1201
16
+ E6
16
= 12E7
16
Data II (12
16
)
Data I (01
16
)
Zero page
Memory
1F
16
Absolute Y
designation
Zero page
indirect
designation
Contents of Index Register Y
Assuming that “01
16
” for Data I, and “12
16
” for Data ll are stored in advance.
