1. Addressing Modes Charles Abzug, Ph.D. Department of Computer Science
James Madison University
Harrisonburg, VA 22807
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© 2002 Charles Abzug

2. Addressing Modes in the Beboputer
Implied: The location(s) acted upon are implied by the instruction mnemonic (the name of the instruction), and therefore are not separately specified. EXAMPLES: INCA #(Increment Accumulator) DECX #(Decrement Index Register) PUSHSR #(Push Status Register) CLRIM #(Clear Interrupt Mask)

3. Figure 8.54 from Maxfield & Brown

4. Addressing Modes in the Beboputer (continued)
Implied: The location(s) acted upon are implied by the instruction mnemonic (the name of the instruction), and therefore are not separately specified. EXAMPLES: INCA #(Increment Accumulator) DECX #(Decrement Index Register) PUSHSR #(Push Status Register) CLRIM #(Clear Interrupt Mask)
Immediate: The value of the operand is specified in the body of the program immediately following the instruction opcode.
EXAMPLES: LDA $F3 #(Load Accumulator)
ADDC % #(Add [to Accumulator] with Carry)
BLDSP $4317 #(“Big” Load Stack Pointer)

5. Figure 8.55 from Maxfield & Brown

6. Addressing Modes in the Beboputer (continued)
Implied: The location(s) acted upon are implied by the instruction mnemonic (the name of the instruction), and therefore are not separately specified. EXAMPLES: INCA #(Increment Accumulator) DECX #(Decrement Index Register) PUSHSR #(Push Status Register) CLRIM #(Clear Interrupt Mask)
Immediate: The value of the operand is specified in the body of the program immediately following the instruction opcode.
EXAMPLES: LDA $F3 #(Load Accumulator)
ADDC % #(Add [to Accumulator] with Carry)
BLDSP $4317 #(“Big” Load Stack Pointer)
Absolute: Instead of the value of the operand, the ADDRESS of the operand follows immediately after the instruction opcode.
EXAMPLES: LDA [DATA] #(Load Accumulator)
LDA [$4317] #(Load Accumulator

7. Figure 8.58 from Maxfield & Brown

8. Addressing Modes in the Beboputer (continued)
Indirect: The address of the address of the operand follows immediately after the instruction opcode. EXAMPLES: LDA [[DATA]] LDA [[$4317]]

9. Figure 8.63 from Maxfield & Brown

10. Addressing Modes in the Beboputer (continued)
Indirect: The address of the address of the operand follows immediately after the instruction opcode. EXAMPLES: LDA [[DATA]] LDA [[$4317]]
Indexed: The value of the Index Register is added to the base address which follows immediately after the instruction opcode. Useful for accessing elements of an array. EXAMPLES: LDA [DATA,X] LDA [$4317,X]

11. Figure 8.65 from Maxfield & Brown

12. Addressing Modes in the Beboputer (continued)
Indirect: The address of the address of the operand follows immediately after the instruction opcode. EXAMPLES: LDA [[DATA]] LDA [[$4317]]
Indexed: The value of the Index Register is added to the base address which follows immediately after the instruction opcode. Useful for accessing elements of an array. EXAMPLES: LDA [DATA,X] LDA [$4317,X]
Pre-Indexed Indirect: The address of the address of the operand is modified by adding the value of the Index Register. EXAMPLES: LDA [[DATA,X]] LDA [[$4317,X]]

13. Figure 8.68 from Maxfield & Brown

14. Addressing Modes in the Beboputer (continued)
Indirect: The address of the address of the operand follows immediately after the instruction opcode. EXAMPLES: LDA [[DATA]] LDA [[$4317]]
Indexed: The value of the Index Register is added to the base address which follows immediately after the instruction opcode. Useful for accessing elements of an array. EXAMPLES: LDA [DATA,X] LDA [$4317,X]
Pre-Indexed Indirect: The address of the address of the operand is modified by adding the value of the Index Register. EXAMPLES: LDA [[DATA,X]] LDA [[$4317,X]]
Indirect Post-Indexed: The value of the Index Register is not added until the second stage of address resolution. EXAMPLES: LDA [[DATA],X] LDA [[$4317],X]

15. Figure 8.69 from Maxfield & Brown

16. Addressing Modes (continued)
ADDITIONAL ADDRESSING MODES COMMONLY USED in digital computers, although not in the Beboputer:
Pre-Indexed Indirect AutoINcrement: Value stored in Index Register is automatically incremented each time the instruction is executed.
Pre-Indexed Indirect AutoDEcrement: Value stored in Index Register is automatically decremented each time the instruction is executed.
Indirect Post-Indexed AutoINcrement: Value stored in Index Register is automatically incremented each time the instruction is executed.
Indirect Post-Indexed AutoDEcrement: Value stored in Index Register is automatically decremented each time the instruction is executed.

17. Op Codes and Addressing Modes
Mnemonic
Implied
Immediate
Absolute
Indexed
Indirect
Pre-Indexed
Post-Indexed
LDA
$90
$91
$92
$93
$94
$95
STA
$99
$9A
$9B
$9C
$9D
JMP
$C1
$C2
$C3
$C4
$C5
JSR
$C9
$CA
$CB
$CC
$CD

18. Summary of Beboputer Addressing Modes
Implied: The location(s) acted upon are implied by the instruction mnemonic (the name of the instruction), and therefore are not separately specified. EXAMPLES: INCA #(Increment Accumulator) DECX #(Decrement Index Register) PUSHSR #(Push Status Register) CLRIM #(Clear Interrupt Mask)
Immediate: The value of the operand is specified in the body of the program immediately following the instruction opcode.
EXAMPLES: LDA $F3 #(Load Accumulator)
ADDC % #(Add [to Accumulator] with Carry)
BLDSP $4317 #(“Big” Load Stack Pointer)
Absolute: Instead of the value of the operand, the ADDRESS of the operand follows immediately after the instruction opcode.
EXAMPLES: LDA [DATA] #(Load Accumulator)
LDA [$4317] #(Load Accumulator

19. Summary of Beboputer Addressing Modes (continued)
Indirect: The address of the address of the operand follows immediately after the instruction opcode. EXAMPLES: LDA [[DATA]] LDA [[$4317]]
Indexed: The value of the Index Register is added to the base address which follows immediately after the instruction opcode. Useful for accessing elements of an array. EXAMPLES: LDA [DATA,X] LDA [$4317,X]
Pre-Indexed Indirect: The address of the address of the operand is modified by adding the value of the Index Register. EXAMPLES: LDA [[DATA,X]] LDA [[$4317,X]]
Indirect Post-Indexed: The value of the Index Register is not added until the second stage of address resolution. EXAMPLES: LDA [[DATA],X] LDA [[$4317],X]

20. Summary of Addressing Modes (continued)
ADDITIONAL ADDRESSING MODES COMMONLY USED, but not in Beboputer
Pre-Indexed Indirect AutoINcrement: Value stored in Index Register is automatically incremented each time the instruction is executed.
Pre-Indexed Indirect AutoDEcrement: Value stored in Index Register is automatically decremented each time the instruction is executed.
Indirect Post-Indexed AutoINcrement: Value stored in Index Register is automatically incremented each time the instruction is executed.
Indirect Post-Indexed AutoDEcrement: Value stored in Index Register is automatically decremented each time the instruction is executed.

21. END