Micro-program Memory Architecture - 20.3.5 | 20. Lecture - 21 | Computer Organisation and Architecture - Vol 2
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Introduction to Micro-programmed Control

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Teacher
Teacher

Welcome everyone! Today we will explore micro-programmed control units. To start, can anyone tell me how micro-programming differs from hardwired control?

Student 1
Student 1

Isn't hardwired control fixed and very fast?

Teacher
Teacher

Absolutely! Hardwired control systems use fixed circuits which generate control signals quickly. However, micro-programmed control systems allow for flexibility as the signals can be programmed. That's a critical distinction.

Student 2
Student 2

So, is flexibility the main advantage?

Teacher
Teacher

Exactly! While micro-programmed systems are slower, they can be reconfigured easily, making them adaptable for various tasks.

Student 3
Student 3

Does that mean the micro-program stores something?

Teacher
Teacher

Yes! Micro-program memory stores the control signals needed for operations, which we can access sequentially or conditionally through a micro-program counter.

Student 4
Student 4

Got it! So, they’re somewhat similar to regular programming?

Teacher
Teacher

Exactly! Micro-programs operate similarly to macros in higher-level programming, with each instruction correlating to specific control operations.

Micro-program Memory and Control Signals

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Teacher
Teacher

Now, let's delve deeper into micro-program memory. Can anyone explain how control signals are accessed?

Student 2
Student 2

I think they are stored in specific memory locations.

Teacher
Teacher

Exactly! Each control signal has a corresponding memory location. When you access that location, the control bits are made either 1 or 0 based on what operations are needed.

Student 1
Student 1

What if I need to jump to another operation?

Teacher
Teacher

Great question! The sequencing is where micro-programmed control becomes intricate. You can’t just move to the next location; you can also jump based on conditions. We adjust the micro-program counter accordingly.

Student 3
Student 3

So, is it like a flowchart where you can branch off?

Teacher
Teacher

Exactly! There are sequential operations that can jump based on conditions, just like branches in a flowchart.

Student 4
Student 4

What about performance? Is it slower like you mentioned?

Teacher
Teacher

Yes, it is slower compared to hardwired systems due to the additional time needed for fetching signals and executing jumps.

Applications and Implications of Micro-programming

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Teacher
Teacher

Let's discuss the applications of micro-programmed control units. Can anyone think of scenarios where flexibility in control signal generation is crucial?

Student 1
Student 1

Maybe in devices that require firmware updates?

Teacher
Teacher

Exactly! Devices like printers and routers benefit from micro-programming, allowing for upgrades without hardware changes.

Student 2
Student 2

What about the disadvantages, though?

Teacher
Teacher

The main disadvantage is speed. While being adaptable is key, if response time is critical, hardwired systems still have the upper hand.

Student 3
Student 3

How does this fit into larger systems?

Teacher
Teacher

In complex systems, micro-programmed control units often complement hardwired controls, managing tasks where flexibility is needed while leaving critical operations to faster systems.

Student 4
Student 4

So it’s all about finding the right balance?

Teacher
Teacher

Precisely! Balance between flexibility and performance is essential in computer architecture.

Introduction & Overview

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Quick Overview

This section explores the concept of micro-programmed control units, emphasizing their structure and function in generating control signals more flexibly compared to hardwired control units.

Standard

Micro-programmed control units operate using a sequence of micro instructions stored in memory, allowing for flexible control signal generation. This section details the workings of micro-program counter, how control signals are established through memory locations, and the significance of sequencing instructions within micro-programs.

Detailed

Micro-program Memory Architecture

This section dives into the crucial aspect of computer architecture known as micro-programmed control units. Unlike hardwired units, where control signals are generated through fixed circuitry, micro-programmed units leverage a memory-based logic system. Each control signal corresponds to a specific memory location, making the control signals programmable and thus flexible. The micro-program itself comprises a sequence of instructions or micro instructions that, when executed, sequentially generate control signals required for various operations.

The section outlines the role of the micro-program memory, which stores these instructions alongside their corresponding control signals. While a hardwired architecture generates these signals rapidly, the micro-programmed approach allows for alterations and flexibility but is typically slower. The navigation within this memory requires a micro-program counter that functions similarly to a traditional program counter in conventional programming, facilitating jumps or conditions that depend on flags.

Overall, the objective is to enable students to understand the architecture and functionality of micro-programmed control units, recognizing their advantages and differences compared to hardwired control mechanisms.

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Introduction to Micro-Programmed Control

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Micro-program control consists of a sequence of instructions, which are micro-programs corresponding to a sequence of micro operations. Control signals are generated using these micro-programmed instructions.

A micro-program control unit is a memory-based system where each memory cell holds control signals for specific micro instructions.

Detailed Explanation

Micro-program control is pivotal in understanding how computer systems generate control signals. Instead of relying solely on hardwired circuits, micro-programming allows for flexibility by storing the necessary control signals in memory. This means that specific actions, represented by micro instructions, can be executed sequentially. By accessing the micro-program memory, a computer can retrieve and generate control signals systematically, enabling various operations without requiring complete re-engineering of the circuitry.

Examples & Analogies

Think of micro-programming like a recipe book for cooking. Each recipe represents a sequence of cooking steps (micro instructions). You can easily access any recipe (micro-program) to cook a dish (perform a micro operation) without changing your kitchen setup (hardware). You only need to read and follow the instructions in your recipe book (micro-program memory) to create different meals.

Micro-Program Memory Structure

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Micro-program memory is similar to normal memory, where control signals are explicitly stored in memory locations. When a specific memory word is accessed, the corresponding control signals are activated (set to 1 or 0) as required for the micro operation.

Detailed Explanation

Micro-program memory functions like a storage system for control signals needed for various micro instructions. Each memory location contains a specific set of control signals, which can be directly fetched as needed. This structure allows for straightforward retrieval and manipulation of control signals, significantly enhancing the processor's efficiency as it can adjust operations without additional circuitry.

Examples & Analogies

Imagine a music playlist on your phone. Each song (memory location) contains specific sounds and notes (control signals) needed to play that song. When you select a song, it plays exactly what is stored without needing to rearrange or change your phone's settings. Similarly, when a computer accesses a micro-program memory location, it directly obtains and executes the associated control signals.

Generation and Sequencing of Control Signals

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Generating control signals in a micro-program is straightforward: you fetch the values from memory, and those values are output as control signals. Sequencing through the micro instructions involves moving from one memory location to the next. However, when a jump instruction is required, the next location must be determined using input signals, making the sequencing slightly complex.

Detailed Explanation

The process of generating control signals is simplified in micro-program architecture. When it's time to execute a micro instruction, the corresponding control signals can be easily retrieved from memory. However, sequencing becomes trickier during operations that require a jump. For example, if certain conditions are met (like checking a flag), the system must know whether to continue in a specific sequence or jump to a different location. This decision-making process requires additional logic, making it more sophisticated compared to sequential memory access.

Examples & Analogies

Think of this like following a treasure map while solving riddles. Each step on the map is like a memory location that tells you where to go next. Generally, you follow the map from one point to another (sequencing). But if the riddle says to jump to a hidden location instead of the next point, you need to decipher what that location is based on clues. This added complexity makes navigating the map (sequencing in the micro-program) a bit more involved yet creative.

Definitions & Key Concepts

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Key Concepts

  • Micro-programmed Control Unit: A control unit architecture that uses stored sequences of instructions to generate control signals.

  • Micro-program Memory: A dedicated memory area for storing micro instructions.

  • Micro-program Counter: A register that keeps track of the current execution point in a micro program.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • In a micro-programmed control unit, executing an ADD instruction could involve fetching control signals that set the ALU for addition.

  • When a conditional branch occurs, the micro-program counter might not increment sequentially but jump to a specific address based on flag conditions.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Micro control units, flexible and true, / Store signals in memory, just like you do.

📖 Fascinating Stories

  • Imagine a library where each book represents a control signal. The librarian chooses the right book based on the needs of the operation, illustrating how a micro-programmed control unit fetches the required signals.

🧠 Other Memory Gems

  • Remember 'C-M-P': Control signals, Memory-based, Programmable for operations.

🎯 Super Acronyms

MPC

  • Micro-Program Counter
  • guiding instruction flow and jumps.

Flash Cards

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Glossary of Terms

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  • Term: Microprogram

    Definition:

    A sequence of micro instructions that defines control signals required for executing operations.

  • Term: Control Signal

    Definition:

    Binary signals used to manage the operations of different components within the computer architecture.

  • Term: Microprogram Memory

    Definition:

    A special memory that stores the micro instructions or control signals for a micro-programmed control unit.

  • Term: Microprogram Counter

    Definition:

    A register that tracks the address of the current micro instruction in the micro-program memory.

  • Term: Hardwired Control

    Definition:

    A control unit architecture that uses fixed circuitry to generate control signals quickly but lacks flexibility.