Immediate Addressing (4.2.1) - Addressing Techniques and Control Unit Design
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Immediate Addressing

Immediate Addressing

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Introduction to Immediate Addressing

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Teacher
Teacher Instructor

Today, we will discuss immediate addressing. It's an addressing mode where the operand is included directly in the instruction. Can anyone give me an example of an immediate addressing instruction?

Student 1
Student 1

Maybe something like `MOV R1, #5`?

Teacher
Teacher Instructor

Exactly! In that instruction, we are moving the constant 5 directly into register R1. Now, why do you think immediate addressing is fast?

Student 2
Student 2

Because it doesn’t have to go fetch the operand from memory?

Teacher
Teacher Instructor

That's right! It saves time because there's no need to access memory; the data is right there in the instruction.

Advantages and Limitations of Immediate Addressing

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Teacher
Teacher Instructor

Now, let’s talk about the advantages. Can anyone tell me why immediate addressing can be beneficial?

Student 3
Student 3

It makes the instructions run faster since they contain all the needed data!

Teacher
Teacher Instructor

That’s right! However, what could be a limitation of including the operand in the instruction?

Student 4
Student 4

I think the size of the operand could be limited, right? Like we can't enter a big number?

Teacher
Teacher Instructor

Exactly! The operand's size is limited by the instruction format. Typically, you can only specify smaller values, limiting its use for larger data.

Use Cases for Immediate Addressing

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Teacher
Teacher Instructor

Can anyone think of situations where immediate addressing would be really useful?

Student 1
Student 1

When you need to do a lot of math with constants, like adding numbers?

Student 2
Student 2

Or when setting a specific value to a register quickly without calculations!

Teacher
Teacher Instructor

Great examples! Immediate addressing is perfect for initializing registers or for straightforward arithmetic operations with constants.

Recap and Key Terms

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Teacher
Teacher Instructor

To summarize, immediate addressing lets us work with constants directly in instructions, allowing for fast execution but with limitations on operand size. Can anyone tell me another term related to immediate addressing?

Student 3
Student 3

Immediate operand size constraints?

Teacher
Teacher Instructor

Great! Understanding these terms and concepts will help you work more effectively with assembly language programming.

Introduction & Overview

Read summaries of the section's main ideas at different levels of detail.

Quick Overview

Immediate addressing directly specifies the operand in the instruction, making it a fast but limited addressing mode.

Standard

Immediate addressing allows a program to use a constant operand specified directly in the instruction. While this addressing mode offers rapid access and execution, its limitation lies in the operand size, restricting the range of values that can be utilized.

Detailed

Immediate Addressing

Immediate addressing is an addressing technique where the operand (i.e., the data to be processed) is directly included within the instruction itself. This method results in quicker execution times since there is no need for additional steps to fetch the operand from memory or registers. However, this efficiency is counterbalanced by limitations concerning the size of the operand—typically constrained by the instruction format. For example, an instruction like MOV R1, #5 initializes register R1 with the constant value 5, showcasing the ease of immediate addressing.

This technique is particularly useful in scenarios where constant values are required, providing a direct and efficient means to use such literals in computations.

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Definition of Immediate Addressing

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Chapter Content

● Operand is directly specified in the instruction.

Detailed Explanation

Immediate addressing is a technique where the operand (the actual value or data to be used in the instruction) is specified directly within the instruction itself. This means that when the instruction is executed, the processor does not need to look up the operand in memory or a register; it can immediately use the value stated in the instruction. This is particularly efficient for small, constant values.

Examples & Analogies

Think of immediate addressing like being given a shopping list that includes specific items at a fixed price. If the list states that 'buy apples for $5', you can physically take apples right away without needing to check current prices at different stores.

Advantages of Immediate Addressing

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Chapter Content

● Fast but limited by operand size.

Detailed Explanation

One of the main advantages of immediate addressing is speed. Since the operand is embedded in the instruction, the processor does not spend time fetching data from memory. However, this technique is limited by the size of the operand specified. For instance, if the instruction format only allows a certain number of bits to represent an operand, the maximum value that can be specified is capped by that bit limit.

Examples & Analogies

Imagine you can only carry a small backpack to a store. You’re fast, but you can only pick up items that fit inside. If there’s a restriction on weight or size, you will miss out on larger or heavier items. Similarly, in immediate addressing, the speed is high, but the size of data that can be directly used is limited.

Example of Immediate Addressing

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Chapter Content

Example: MOV R1, #5

Detailed Explanation

In this example, the instruction 'MOV R1, #5' moves the value '5' directly into the register 'R1'. The '#' symbol indicates that '5' is an immediate value rather than a memory address. Thus, upon execution, the processor sees '5' right in the instruction, allowing it to quickly store that value in register 1 without needing to access memory.

Examples & Analogies

Imagine writing down your name on a form without needing to refer to your driver's license. You instantly put your name on the form, which is like using immediate addressing where you see the value right there and don’t have to look it up somewhere else.

Key Concepts

  • Immediate Addressing: A method of specifying the operand within the instruction, allowing for rapid execution.

  • Operand Size Limitations: The specific size of operands is constrained by the instruction format, limiting its effectiveness.

Examples & Applications

Instruction: MOV R1, #10 - Moves the value 10 directly into register R1.

Instruction: ADD R2, #5 - Adds 5 to the value in register R2.

Memory Aids

Interactive tools to help you remember key concepts

🎵

Rhymes

Immediate, oh so neat, operands directly to greet!

📖

Stories

Imagine a toolbox where every tool needed is laid out – immediate addressing is like having your favorite hammer right on top, ready to grab without searching!

🧠

Memory Tools

I - Instruction has Operator Directly and Efficiently (= Immediate addressing).

🎯

Acronyms

I for Immediate = Instantly in Instruction.

Flash Cards

Glossary

Immediate Addressing

An addressing mode where the operand is directly specified in the instruction.

Operand

The part of an instruction that specifies the data to be operated on.

Instruction

A binary-encoded command that the CPU can execute.

Reference links

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