Page 74 - Computer_Science_F5

Addressing modes Direct addressing
In the previous section, we learned The instruction specifies a memory
about the instruction cycle. We saw address where the data is stored. Chapter One: Computer architecture
how instructions are fetched, decoded,
and their operations are carried Example (MIPS): lw $t2, 10($s0) (Loads
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out. Addressing modes are special data from the memory location 10 bytes
instructions that help the CPU find data. away from the address in $s0 into $t2).

Recall the kitchen-ISA analogy introduced Indirect addressing
at the beginning of this chapter. Imagine The instruction specifies a memory
you are a chef following a recipe (the address that points to another memory
program) in a kitchen (the CPU). The location with the actual data.
recipe tells you what ingredients (data)
to use and what steps (instructions) to Example (MIPS): lw $t4, ($s5) (Loads
take. But how does the recipe tell you data from the memory location pointed
exactly where to find those ingredients? to by the address in $s5 into $t4).
This is where addressing modes come
in – they are like special instructions Relative addressing
within instructions, telling the CPU The instruction specifies an offset from
how to locate the data it needs to work the current instruction’s address.
with. Common addressing modes are;
register addressing, immediate addressing, Example (MIPS): beq $t6, $s7, Label
direct addressing, indirect addressing and (Branches to “Label” if the values in $t6
relative addressing. and $s7 are equal, using an offset relative
to the current instruction’s address).
Register addressing

Data is stored in registers within the Exercise 1.14
CPU, providing fast and efficient access.
Example (MIPS): add $t1, $s2, $s3 Imagine you are a programmer
(Adds values in registers $s2 and $s3, working on a game engine for a
storing the result in $t1). mobile racing game. The game
uses various data structures to store
Immediate addressing information about the race track, car
The instruction includes the actual data physics, and player input. Answer the
value. following questions, considering the
most appropriate addressing mode
Example (MIPS): addi $t0, $s1, 5 (Adds (register, immediate, direct, indirect,
5 to the value in register $s1, storing the or relative) for each scenario and
result in $t0). explain your reasoning.

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Student’s Book Form Five

Computer Science Form 5.indd 65 23/07/2024 12:32