LOAD INDIRECT
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Understanding LOAD IMMEDIATE
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today, we start with LOAD IMMEDIATE, which is denoted as LDI. Can anyone tell me what this instruction does?
Does it load a value directly into the accumulator?
Exactly! For example, using LDI 20 loads the binary equivalent of 20 directly into the accumulator.
So there's no need to access a memory location?
Correct! This is efficient since the value is part of the instruction itself. Remember, LDI = Load Direct Immediate.
How does this compare to LOAD DIRECT?
Great question! LOAD DIRECT references a specific memory location instead of embedding the value. For instance, LOAD ACCUM 3 retrieves the content from memory location 3 instead of loading a fixed value.
So, LDI is faster because it skips extra steps?
Exactly! Less overhead means quicker execution. Let's summarize: LDI directly loads a fixed value, while LOAD DIRECT fetches data from memory.
Exploring LOAD INDIRECT
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now let’s move on to LOAD INDIRECT, say LOAD INDIRECT 5. What does this do?
It loads the accumulator with a value from a memory address that is found in another memory location?
Spot on! Here, you access memory location 5, which might hold the address of another location, say location 1. What could be there?
The value stored there, like 49?
Exactly! The process involves first retrieving an address and then accessing it—this is an example of indirection.
Is this common in all processors?
Yes, while the mechanisms may differ, indirect addressing is widely utilized across various architectures for efficiency and flexibility.
Can you give an example where indirect addressing is useful?
It’s great for accessing arrays where the elements are stored in contiguous memory. Instead of calculating offsets, you can just point to the starting address.
Displacement Addressing Explained
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Let's dive into displacement addressing. What do we mean by this term?
Is it where we combine values from memory and registers to calculate an address?
Precisely! Displacement involves adding a value from a register to a fixed memory address to get the effective address.
Are there specific types of displacement addressing?
Yes! Some include relative addressing, where the program counter is used, and base register addressing, which uses a specified register instead.
Could you explain how relative addressing works?
Of course! In relative addressing, you take the current value of the PC, add a displacement value, and locate the target data. It's widely used for jumps in code execution.
That makes sense! And base registers are for more flexible memory management, right?
Exactly! It’s vital when dealing with dynamic data structures like linked lists. Remember: Displacement = Register + Memory Address.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, we explore several addressing modes including LOAD IMMEDIATE, LOAD DIRECT, LOAD INDIRECT, REGISTER DIRECT, and their operational implications. Detailed examples illustrate how these operations manipulate data in memory and registers, highlighting the mechanics of indirect addressing and displacement addressing modes.
Detailed
LOAD INDIRECT: Addressing Modes Overview
This section explains crucial addressing modes in computer architecture that regulate how data is accessed and manipulated in memory, focusing on the relationship between memory locations, registers, and instructions.
- LOAD IMMEDIATE (LDI): This instruction directly loads a value (e.g., 20) into the accumulator without referencing any memory location, as the value is embedded in the instruction itself. Hence, there's no latency from memory access, which makes this addressing mode efficient for constant assignments.
- LOAD DIRECT: An instruction like LOAD ACCUMULATOR 3 signifies that the accumulator will be loaded with the data from memory location 3. In our case, if memory location 3 contains 20, the accumulator reflects this value, which implies quick access based on direct addressing.
- LOAD INDIRECT: For LOAD INDIRECT 5, the instruction provides an address that points to another address. In this case, the instruction accesses memory location 5, retrieves its content (which is the address of memory location 1 that holds 49), and loads this value into the accumulator. This involves a two-tier access method, emphasizing the indirection concept in addressing modes.
- REGISTER-BASED MODES: Various forms utilize registers—LOAD REGISTER DIRECT and REGISTER INDIRECT—relating to different methods of data loading. The latter uses the contents of a register as an address, drawing direct data from memory.
- Displacement Addressing Modes: We explore more dynamic addressing techniques, particularly displacement addressing, where two values are summed (one from a register and one from a memory address) to determine the effective address of the operand. Different variations include relative addressing (utilizing the program counter), base register addressing, and indexed addressing.
By learning these addressing modes, one can understand underlying principles guiding how computer systems efficiently handle data access, crucial for performance optimization.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Understanding LOAD INDIRECT
Chapter 1 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
LOAD INDIRECT 5. Now this is interesting. LOAD INDIRECT 5 means accumulator will be loaded with something which is present in memory location 5. Memory location 5 has value 1. Now it’s an indirect addressing mode. So, 1 is not the data; the data is actually present in memory location 1. So, what is in memory location 1? Present is 49. So, the 49 will be stored in your accumulator.
Detailed Explanation
The LOAD INDIRECT instruction allows the CPU to load a value indirectly from memory. When you execute LOAD INDIRECT 5, the CPU first looks at memory location 5. It finds the value 1 there, and instead of using 1 directly, it treats it as an address. It then goes to memory location 1 to retrieve the actual data, which is 49 in this case, and loads it into the accumulator. This two-step process is what defines indirect addressing.
Examples & Analogies
Think of it like a library system. You have a book with an address on it (memory location 5) that tells you where to find another book (memory location 1). Instead of reading the first book directly, you go to the address listed, which leads you to the actual book you need (the value 49).
Direct vs. Indirect Addressing
Chapter 2 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
LOAD DIRECT 3 is a direct addressing mode. Direct addressing means that 3 actually refers to memory location 3, where the data is present. LOAD ACCUMULATOR 3 means you load into the accumulator what is present in memory location 3, which is 20.
Detailed Explanation
In direct addressing mode, the instruction points directly to the data in memory. When executing LOAD DIRECT 3, the CPU accesses memory location 3 directly, retrieves the value (20), and loads it into the accumulator. This is different from indirect addressing where the instruction first retrieves an address from a designated memory location before finding the corresponding value.
Examples & Analogies
Imagine you have a box labeled 'Toaster' (LOAD DIRECT 3) that directly takes you to the appliance. You open it and find a toaster (value 20) inside ready to use, rather than needing to look somewhere else first to find out what you should use.
Registry Indirect Addressing Concept
Chapter 3 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
REGISTER INDIRECT 2 means register 2 has a value of 3. In this case, we don't use 3 directly to get data. Instead, we first access memory location 3 because it holds the content we'd like (20). So, we end up loading 20 into the accumulator just like with LOAD INDIRECT.
Detailed Explanation
Register indirect addressing utilizes the value in a register to determine a memory address. When executing REGISTER INDIRECT 2, the CPU checks register 2 for its value (3), then goes to memory location 3, retrieves the value stored there (20), and loads it into the accumulator. This method allows for more flexibility in memory addressing since registers can be dynamically changed during execution.
Examples & Analogies
Consider a situation where you have a key (the register value) for a drawer (memory location 3). Instead of knowing the drawer's contents directly (the value 20), you first check the key (the register value) to open the drawer and find what is inside.
Displacement Addressing Mode
Chapter 4 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Wherever you talk about displacing, you will find two components in the addresses that are used together to get the effective one. One is an explicit address of main memory, and the other refers to a register whose content adds to that explicit address to obtain the effective address.
Detailed Explanation
Displacement addressing combines an explicit memory address with the contents of a register to calculate the final address where the data resides. For instance, if the memory location is 3 and the register contains the value 2, adding them together gives an effective address of 5 (3 + 2). The CPU will then access this computed address to retrieve the value stored there.
Examples & Analogies
Think about mailing a letter. If you have an address (the explicit memory address) but live two blocks away (the register's value), you would walk the two blocks to reach the intended address where your letter should go. Therefore, the final destination combines both the address on the envelope and your location's contribution.
Applications of Displacement Addressing
Chapter 5 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
For loops, you can access many memory locations one after the other by just changing the register's value by 1. This is useful for arrays stored in contiguous locations.
Detailed Explanation
Displacement addressing is particularly useful in programming constructs like loops and arrays. By incrementing the value of a register, you can modify the address from which data is drawn sequentially. For instance, starting at a base address and incrementing by one allows you to traverse through each element of an array stored in consecutive memory locations.
Examples & Analogies
Imagine a train with several carriages (the array). If you have a ticket (the base address) that indicates where to start, and as you move from one carriage to the next each time you step forward (each increment of the register), you can easily visit every carriage one after another without confusion.
Key Concepts
-
Load Immediate (LDI): Refers to directly loading a specified constant value into an accumulator without accessing memory.
-
Load Direct: Involves loading data from a specific memory address into the accumulator.
-
Load Indirect: Accesses data via a memory address contained within another address, demonstrating indirection in address resolution.
-
Displacement Addressing: Combines values from both a memory address and register to determine an effective address, providing flexibility in accessing data.
Examples & Applications
LOAD IMMEDIATE 20 loads the number 20 directly into the accumulator, while LOAD DIRECT 3 loads the value from memory location 3 into the accumulator.
LOAD INDIRECT 5 accesses memory location 5 to retrieve the address of memory location 1 (which could have a value of 49) and loads this value into the accumulator.
In displacement addressing, if R2 contains 3 and the base memory reference is 5, the effective address becomes 5 + 3 = 8, and the instruction retrieves data from this address.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
LOAD IMMEDIATE is so neat, constant in the instruction, quite a treat!
Memory Tools
Recall LDI (Load Direct Immediate) is quick and neat; while for LOAD INDIRECT, check memory for a treat.
Acronyms
Remember LDI, LOD, and LODI
The modes of fetching
handy when coding!
Flash Cards
Glossary
- Load Immediate (LDI)
An instruction that loads a constant value directly into the accumulator from the instruction itself.
- Load Direct
An instruction that loads a value from a specified memory location into the accumulator.
- Load Indirect
An instruction that loads a value into the accumulator from a memory address referenced in another memory location.
- Displacement Addressing
A technique that calculates an effective address by combining a fixed memory address with a register value.
- Base Register
A type of register that holds a memory address which can be commonly used with displacement addressing.
- Relative Addressing
An addressing mode that uses the contents of the program counter to determine the effective address.
- Indexed Addressing
An addressing mode that uses a general-purpose register to provide an offset for data access.
Reference links
Supplementary resources to enhance your learning experience.