1. Mod-Mod Pengalamat Segera (Immediate) Terus (Direct)
Tak terus (Indirect)
Daftar (Register)
Daftar tak terus (Register indirect)
Penggantian (Displacement - (indexed)) 2

2. Immediate Addressing Operan adalah sebahagian daripada arahan
Operand = address field
e.g. ADD 5
=> ADD #5 => AC = AC + 5
Tambah 5 kepada kandungan accumulator
5 adalah operan
Tiada rujukan memori untuk mengambil data
Pantas
Julat yang terhad
Instruction
Opcode
Operand 3

3. Direct Addressing
Medan alamat (address field) mengandungi alamat bagi operan
Alamat efektif = alamat medan
(Effective address (EA) = address field (A))
Cth ADD A
Tambah kandungan bagi sel A kepada penumpuk (accumulator)
Cari operan dalam memori pada alamat A
Rujukan memori tunggal untuk mengakses data
Tiada tambahan congakkan untuk mendapatkan EA
Ruang alamat terhad 5

4. Direct Addressing Diagram
Instruction
Opcode
Address A
Memory
Operand
=> Load a => ac <= a 6

5. Indirect Addressing (1)
Memory cell pointed to by address field contains the address of (pointer to) the operand
EA = (A)
Look in A, find address (A) and look there for operand
e.g. ADD (A)
Add contents of cell pointed to by contents of A to accumulator
=> Add a, (b) => a = a+ (b) 7

6. Indirect Addressing (2)
Large address space
2n where n = word length
May be nested, multilevel, cascaded
e.g. EA = (((A)))
Multiple memory accesses to find operand
Hence slower 8

7. Indirect Addressing Diagram
Instruction
Opcode
Address A
Memory
Pointer to operand
Operand 9

8. Register Addressing (1)
Operand is held in register named in address filed
EA = R
=> ADD R1, R2
=> R1 = r1 + r2
Limited number of registers
Very small address field needed
Shorter instructions
Faster instruction fetch 10

9. Register Addressing (2)
No memory access
Very fast execution
Very limited address space
Multiple registers helps performance
Requires good assembly programming or compiler writing
N.B. C programming
register int a;
c.f. Direct addressing
cf. is an abbreviation from a Latin word (confer) and means 'refer to' or 'compare with'
N.B = nota bene - Used to direct attention to something particularly important 11

10. Register Addressing Diagram
Instruction
Opcode
Register Address R
Registers
Operand 12

11. Register Indirect Addressing
C.f. indirect addressing
EA = (R)
Operand is in memory cell pointed to by contents of register R
Large address space (2n)
One fewer memory access than indirect addressing 13

12. Register Indirect Addressing Diagram
Instruction
Opcode
Register Address R
Memory
Registers
Pointer to Operand
Operand 14

13. Displacement Addressing
EA = A + (R)
Address field hold two values
A = base value
R = register that holds displacement
or vice versa 15

14. Displacement Addressing Diagram
Instruction
Opcode
Register R
Address A
Memory
Registers
Pointer to Operand +
Operand 16

15. Relative Addressing A version of displacement addressing
R = Program counter, PC
EA = A + (PC)
i.e. get operand from A cells from current location pointed to by PC
c.f locality of reference & cache usage 17

16. Base-Register Addressing
A holds displacement
R holds pointer to base address
R may be explicit or implicit
e.g. segment registers in 80x86 18

17. Indexed Addressing A = base R = displacement EA = A + R
Good for accessing arrays
R++ 19

18. Combinations
Postindex
EA = (A) + (R)
Preindex
EA = (A+(R)) 20

19. Stack Addressing Operand is (implicitly) on top of stack e.g.
ADD Pop top two items from stack and add 21