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A short class with Sarah and her students. The other ways are under More.
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Today, we will explore immediate and non-immediate addressing. Can anyone tell me what 'immediate addressing' means?
Is it when the value is included directly in the instruction itself?
Correct, Student_1! When using immediate addressing, the operand value is right there with the instruction. For example, if we have 'ADD 5', it means add 5 directly. Now, how about non-immediate addressing?
Does it mean we have to get the value from a memory location instead?
Exactly! If the instruction is 'ADD M5', it means we need to fetch the value from memory location 5 first. Remember, immediate is 'now,' while non-immediate is 'later.'
Can we use immediate addressing for all data?
Great question, Student_3! Immediate addressing is usually limited to smaller values that fit directly into the instruction. For larger data, we rely on non-immediate addressing.
In essence, to remember: Immediate is 'immediate access,' while non-immediate is 'fetch from memory.'
Now that we understand addressing types, let’s talk about interrupts. What do you think happens during an interrupt?
Isn't it when the CPU stops its current task to handle a special request?
Exactly, Student_2! When an interrupt occurs, the CPU needs to stop executing its current task. So, what does it do with the program counter, PC?
Does it save the PC’s current value somewhere before jumping to the interrupt service routine?
That's right! The CPU saves the current PC value on the stack so it can return to where it left off after servicing the interrupt. This ensures the program can continue smoothly.
What exactly is the interrupt service routine?
Good question, Student_1! The ISR is a special block of code designed to handle the specific task caused by the interrupt. Once that's done, the CPU restores the PC, and processing continues from where it left off.
Remember, interrupts are essential for handling events that require immediate attention while maintaining a smooth flow of processing.
Next, let’s delve into the Instruction Cycle Code, or ICC. Can someone explain what ICC indicates?
Isn't it a code that tells us the current phase of instruction execution—like fetch or execute?
Exactly! The ICC gives us a clear indication of whether we're fetching, decoding, executing, or servicing an interrupt. For instance, if ICC is 00, we’re fetching.
What do we know if the ICC shows 10?
That means the instruction is ready to execute. If we see 01, it means we are in the operand fetch phase, and 11 designates the interrupt handling phase.
So, this code helps us track what’s going on during instruction execution?
Precisely, Student_2! The ICC acts like a traffic signal for the CPU, guiding it in which phase it operates.
To remember the phases: Imagine 'F-D-E-I' - Fetch, Decode, Execute, Interrupt!
Operand's value is directly included in instruction.
Operand is referenced via memory locations.
Mechanism to temporarily pause execution for prioritized tasks.
Keeps track of the current execution location.
Code executed in response to an interrupt.
Binary indicator of the current instruction phase.
If it’s there in plain sight, immediate feels right; fetch from memory’s plight, non-immediate takes flight.
Imagine a student who has a math question in class—when they have the answer in their notes, they share it right away (immediate). But if they need to look it up from their locker (non-immediate), it takes more time.
Think 'I NOW' for Immediate and 'N-M' for Non-immediate. 'N-M' is like 'Need Memory' to remind you that it’s fetched from memory.
For interrupts, remember 'SIR' - Save, Interrupt, Return. Save the PC state, handle the interrupt, then return to the prior task.
Term
Immediate Addressing
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Term
Non-immediate Addressing
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Term
Interrupt
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Term
Program Counter
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Term
Interrupt Service Routine
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A mode in which the operand's value is directly specified in the instruction.
A mode where the operand is not directly specified; it must be fetched from a memory location.
An event that temporarily halts the current instruction to allow servicing a higher-priority task.
A block of code designed to handle specific tasks triggered by interrupts.
A register that keeps track of the next instruction to be executed.
A binary code indicating the current phase of instruction execution — Fetch, Decode, Execute, or Interrupt.
This section discusses the concepts of immediate and non-immediate addressing in instruction execution and the functionality of interrupt servicing.
The section explains the difference between immediate addressing, where operand values are part of the instruction, and non-immediate addressing, where they are referenced in memory. It also outlines the process of handling interrupts during instruction execution, including the management of the program counter and register values.
In computer architecture, addressing modes are essential for determining how the CPU recognizes and accesses data. This section elaborates on two types of addressing: immediate and non-immediate.
Immediate Addressing: In immediate addressing, the operand's value is embedded directly within the instruction itself. For example, in an instruction like ADD ACCUMULATOR, 32, the number 32 is a value that will be immediately added to the accumulator without needing to reference another memory location.
Non-immediate Addressing: Conversely, non-immediate addressing requires fetching the operand from a memory location. For instance, ADD ACCUMULATOR, M32 means retrieving the value stored at memory location 32 before performing the addition.
The section also highlights the execution cycle of instructions, especially how the CPU handles interrupts. When an interrupt occurs, the CPU saves the current state of the program counter (PC) and other relevant registers on the stack, allowing it to jump to an interrupt service routine (ISR) before returning to the original instruction flow once the interruption has been addressed. The instruction cycle code (ICC) further supports this process, indicating the current phase of instruction execution (fetch, decode, execute, or interrupt). Overall, understanding these addressing types and interrupt management is critical for effective CPU operation.