Motorola HC12 User Manual

Assembler Syntax

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MCUez HC12 Assembler

User’s Manual

MOTOROLA

Assembler Syntax

143

7.4.3.15  Indexed-Indirect, D Accumulator Offset

This addressing mode adds the value in D to the base index register. This forms
the memory address containing a pointer to the memory location referenced in
the instruction. The base index register may be X, Y, SP, or PC.

Example:

entry1:     NOP

            NOP

entry2:     NOP

            NOP

entry3:     NOP

            NOP

main:

            LDD  #2

            JMP  [D, PC]

goto1:      DC.W entry1

goto2:      DC.W entry2

goto3:      DC.W entry3

This example represents a jump table. The values beginning at

goto1

 are

potential destinations for the jump instruction.

When

JMP [D, PC]

is executed,

PC

 points to

goto1

 and

D

 holds the

value 2.

The

JMP

instruction adds the value in

D

and

PC

to form the address of

goto2

.

The CPU reads the address stored there (the address of label entry2) and jumps
to that location.