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LEAX
Effective Address ⇒ X
Operation:
Description:
Loads index register X with an effective address specified by the pro-
gram. The effective address can be any indexed addressing mode oper-
and address except an indirect address. Indexed addressing mode
operand addresses are formed by adding an optional constant supplied
by the program or an accumulator value to the current value in X, Y, SP,
or PC. See
Operation is a bit more complex when LEAX is used with auto-increment
or auto-decrement operand specifications and index register X is the ref-
erenced index register. The index register is loaded with what would
have gone out to the address bus in the case of a load indexed instruc-
tion. In the case of a pre-increment or pre-decrement, the modification is
made before the index register is loaded. In the case of a post-increment
or post-decrement, modification would have taken effect after the ad-
dress went out on the address bus, so post-modification does not affect
the content of the index register.
Condition Codes and Boolean Formulas:
S
–
None affected.
Addressing Modes, Machine Code, and Execution Times:
Source Form
LEAX oprx0_xysp
LEAX oprx9,xysp
LEAX oprx16,xysp
Notes:
1. Due to internal CPU requirements, the program word fetch is performed twice to the same address during this
instruction.
CPU12
REFERENCE MANUAL
Load X with Effective Address
3.8 Indexed Addressing Modes
X
H
I
N
Z
–
–
–
–
–
Address Mode
IDX
1A xb
IDX1
1A xb ff
IDX2
1A xb ee ff
INSTRUCTION GLOSSARY
for more details.
V
C
–
–
Object Code
LEAX
Cycles
Access Detail
1
2
PP
2
PO
2
PP
MOTOROLA
6-129
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