4/17/98 6-107 Addressing Modes and Data Types
LEA Load effective address
Syntax: LEA Rd, Rs+offset8/16
Operation: (Rd) <-- (Rs)+offset8/16
Description: The word specified by the source operand is added to the offset value and the result
is stored into the register specified by the destination operand. The source and destination operands
are both registers. The offset value is an immediate data field of either 8 or 16 bits in length. The
source data is not affected by the operation.
This instruction mimics the address calculation done during other instructions when the register
indirect with offset addressing mode is used, allowing the resulting address to be saved for other
purposes.
Note: The result of this operation is always a word since it duplicates the calculation of the indirect
with offset addressing mode.
Size: Word-Word
Flags Updated: none
LEA Rd, Rs+offset8
Bytes: 3
Clocks: 3
Encoding:
byte 3: offset8
LEA Rd, Rs+offset16
Bytes: 4
Clocks: 3
Operation: (Rd) <-- (Rs)+offset16
Encoding:
byte 3: upper 8 bits of offset16
byte 4: lower 8 bits of offset16
0 1 0 0 0 0 0 0 0 d d d 0 s s s
0 1 0 0 1 0 0 0 0 d d d 0 s s s
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