Part A: Interrupt Handling (8085) - 3.1 | EXPERIMENT NO. 5 TITLE: Interrupt Handling and Timer Interfacing (8085/8086 Microprocessors with 8253/8254 Timer) | Microcontroller Lab
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Knowledge

3.1 - Part A: Interrupt Handling (8085)

Practice

Interactive Audio Lesson

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Definition of Interrupts

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0:00
Teacher
Teacher

Let's talk about interrupts. An interrupt is a signal that tells the CPU that an event needing immediate action has occurred. Can anyone tell me why this is important?

Student 1
Student 1

It allows the CPU to handle events without constantly checking all devices!

Teacher
Teacher

Exactly! This is known as event-driven processing. It frees up CPU time for other tasks. Now, can anyone think of some examples of events that might trigger interrupts?

Student 2
Student 2

A key press or a timer reaching zero?

Teacher
Teacher

Right! Those are perfect examples. Remember, interrupts help multitasking and handle errors efficiently.

Types of Interrupts

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0:00
Teacher
Teacher

Now, let's discuss the types of interrupts. The 8085 can handle hardware and software interrupts. Can anyone tell me the difference between these two?

Student 3
Student 3

Hardware interrupts are triggered by external devices, while software interrupts are caused by specific instructions in the code.

Teacher
Teacher

Very good! And we also have maskable and non-maskable interrupts. Who can explain the difference?

Student 4
Student 4

Maskable interrupts can be turned off by the CPU, but non-maskable interrupts cannot.

Teacher
Teacher

Exactly! Non-maskable interrupts are usually reserved for critical events. This distinction is crucial for effective interrupt management.

Interrupt Handling Process

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Teacher
Teacher

Let's walk through the interrupt handling process. What happens when an interrupt occurs in the microprocessor?

Student 1
Student 1

The current instruction finishes executing, and then the CPU saves its context.

Teacher
Teacher

Correct! Then the CPU looks for the address of the ISR. What does ISR stand for?

Student 2
Student 2

Interrupt Service Routine!

Teacher
Teacher

Exactly. After executing the ISR, the CPU restores its context and resumes the main program where it left off. This allows for seamless processing.

Specifics of 8085 Interrupts

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Teacher
Teacher

The 8085 has specific hardware interrupt pins like TRAP and RST 7.5. What do you think is the significance of their priorities?

Student 3
Student 3

Higher priority interrupts are serviced first, allowing more critical events to be handled immediately.

Teacher
Teacher

Exactly! And to manage these interrupts, we use the SIM instruction. Can anyone fill me in on what SIM does?

Student 4
Student 4

It sets the interrupt mask and defines which maskable interrupts are enabled or disabled.

Teacher
Teacher

Perfect! Knowing how to configure these interrupts is essential for developing reliable systems.

Return from Interrupt

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0:00
Teacher
Teacher

Finally, how do we return from an ISR?

Student 1
Student 1

The RET instruction is used.

Teacher
Teacher

Correct! It's also important to restore any registers before returning to ensure the main program is unaffected. Why is this crucial?

Student 2
Student 2

To avoid errors in the main program's execution!

Teacher
Teacher

Exactly! This ensures smooth operation and reliability of the system. Interrupts are a powerful feature of microprocessors when handled correctly.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section covers interrupt handling in the 8085 microprocessor, including the types of interrupts, their purposes, and how to manage them effectively.

Standard

The section explores the concept of interrupts as a mechanism for managing events in microprocessors. It details the different types of interrupts, including hardware and software interrupts, outlines the interrupt handling process in the 8085 microprocessor, and provides specific instructions for managing interrupts with a focus on hardware interrupts and the setting up of an interrupt service routine (ISR).

Detailed

Interrupt Handling in 8085

Overview

Interrupts are crucial for the efficient operation of microprocessors like the 8085, allowing them to pause their current tasks and respond to events or conditions requiring immediate attention.

Key Concepts

  1. Definition of Interrupt: An interrupt is a signal from a peripheral device or software that indicates an event requiring immediate CPU attention.
  2. Types of Interrupts: The 8085 supports hardware interrupts (triggered by external signals) and software interrupts (triggered by specific instructions). It further categorizes interrupts as maskable and non-maskable based on whether they can be disabled by software.
  3. Interrupt Handling Procedure: When an interrupt occurs, the current instruction completes, the CPU saves its context, and control is transferred to the appropriate ISR. This allows multitasking and error handling without constant checking of devices.
  4. Specifics of the 8085 System: The 8085 has various interrupt pins (e.g., TRAP, RST 7.5) with specific priorities and vector addresses. The SIM instruction is important for managing maskable interrupts, controlling which interrupts are active.
  5. Terminating the ISR: The process includes executing the ISR, restoring the context, and returning control back to the original program.

Understanding these aspects of interrupt handling in the 8085 microprocessor is foundational for programming and creating responsive applications and embedded systems.

Audio Book

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Overview of Interrupts

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An interrupt is a signal to the microprocessor from a peripheral device or a software instruction that indicates an event has occurred and requires immediate attention. When an interrupt occurs, the microprocessor temporarily suspends its current program execution, saves its current state (context), jumps to a special routine called an Interrupt Service Routine (ISR) or Interrupt Handler, executes the ISR, and then returns to the original program at the point where it was interrupted.

Detailed Explanation

An interrupt acts as an alert for the microprocessor, indicating that something important needs its attention. When an interrupt is received, the microprocessor pauses what it's doing, saves its current situation (like a bookmark), goes to a special function (the ISR), and once that task is done, it goes back to where it left off. This process helps in handling multiple tasks efficiently.

Examples & Analogies

Imagine you're in the middle of a conversation with a friend when someone taps you on the shoulder and asks for your help. You pause your conversation, help that person (your ISR), and then return to your friend to continue where you left off. This is similar to how interrupts work in a microprocessor.

Purpose of Interrupts

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  1. Event-Driven Processing: Allows the CPU to respond to external events (e.g., key press, data arrival, timer expiry) efficiently without constantly polling devices, freeing up CPU time for other tasks.
  2. Multitasking/Time-sharing: Enables operating systems to switch between tasks or share CPU time among multiple programs.
  3. Error Handling: Used to handle critical errors like power failures or division-by-zero.

Detailed Explanation

Interrupts serve several vital roles in a microprocessor's operation. They enable the CPU to be responsive to events like user inputs, allowing it to pause its current task without wasting time on constant checks. This supports multitasking, where multiple programs can run efficiently without interfering with one another. Additionally, they assist in managing errors, ensuring that critical issues can be attended to immediately.

Examples & Analogies

Think of a teacher managing a classroom. Instead of continuously checking every student's work, they can focus on teaching while being alerted by raised hands (interrupts) from students who need help. This streamline allows for effective management of time and tasks.

Types of Interrupts

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  • Hardware Interrupts: Triggered by an external hardware signal from a peripheral device (e.g., keyboard, timer, sensor).
  • Software Interrupts: Triggered by a specific instruction in the program (e.g., INT instruction in 8086, RST instructions in 8085 used as software interrupts).
  • Maskable Interrupts: Can be enabled or disabled (masked) by software instructions.
  • Non-Maskable Interrupts (NMI): Cannot be disabled by software.
  • Vectored Interrupts: The CPU automatically jumps to a predefined memory location for the ISR.
  • Non-Vectored Interrupts: The interrupting device needs to be determined through polling.

Detailed Explanation

Interrupts can be classified into several types. Hardware interrupts come from external devices, like keyboards, while software interrupts are initiated by the program itself. Maskable interrupts can be temporarily ignored by the CPU if needed, but non-maskable interrupts require immediate attention. Vectored interrupts streamline the process by directing the CPU straight to the routine needed for the interrupt.

Examples & Analogies

Consider a mobile phone. When someone calls, that's like a hardware interrupt. If a friend sends a message while you're using an app, that's a software interrupt. You can decide to ignore incoming calls (maskable interrupt) or emergencies (non-maskable interrupt). Detecting who's calling allows you to direct attention as needed (vectored interrupt).

Interrupt Process Flow

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  1. Interrupt Occurs: A hardware signal or software instruction triggers an interrupt.
  2. Current Instruction Completion: The CPU finishes executing the instruction it is currently working on.
  3. Context Saving: The CPU's current state (Program Counter, Flag Register, etc.) is automatically pushed onto the stack.
  4. Vectoring: The CPU determines the starting address of the appropriate ISR.
  5. ISR Execution: The CPU jumps to the ISR and executes its instructions.
  6. Context Restoration: The saved CPU state is popped from the stack.
  7. Return from Interrupt: An RET or IRET instruction returns control to the main program.

Detailed Explanation

When an interrupt is received, a series of steps are followed. First, the interrupt signal is recognized. The CPU finishes the instruction it is currently executing so that it can switch tasks neatly. It saves its current state, so nothing is lost, and then it determines which Interrupt Service Routine to run. After executing the ISR, the CPU restores its saved state and continues from where it was interrupted. This structured flow ensures smooth transitions between tasks.

Examples & Analogies

Imagine a chef cooking a meal when suddenly the fire alarm goes off (interrupt). The chef finishes chopping an onion (completes the current task), writes down what they were doing (saves context), heads to the fire alarm to investigate (executes ISR), and when everything is safe, goes back to finish the meal (return from interrupt). This sequence keeps everything organized and efficient.

Interrupt Handling in 8085

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The 8085 has 5 hardware interrupt pins and can also handle software interrupts. The hardware interrupt pins (from highest to lowest priority) are:
1. TRAP (Non-Maskable, Vectored): Highest priority, jumps to address 0024H.
2. RST 7.5: Edge triggered, jumps to address 003CH. Maskable.
3. RST 6.5: Level triggered, jumps to address 0034H. Maskable.
4. RST 5.5: Level triggered, jumps to address 002CH. Maskable.
5. INTR (Maskable, Non-Vectored): Requires external hardware to provide vector address.

Detailed Explanation

The 8085 microprocessor has multiple interrupt pins that handle external signals. Each pin has a different priority level and behaves differently. TRAP has the highest priority and cannot be ignored, while others like RST 7.5 can be masked or ignored by the program, allowing flexibility in handling interrupts based on the system's needs.

Examples & Analogies

It’s like a busy manager receiving requests. The most urgent requests (TRAP) must be handled immediately, while less urgent matters (RST 7.5 or 6.5) can be deferred if needed, allowing the manager to prioritize tasks effectively.

Controlling Maskable Interrupts

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To control maskable interrupts, the 8085 utilizes:
* EI (Enable Interrupts): Allows maskable interrupts to be processed.
* DI (Disable Interrupts): Prevents maskable interrupts from being processed.
* SIM (Set Interrupt Mask): Configures which maskable interrupts are enabled or disabled.

Detailed Explanation

The management of maskable interrupts is crucial for ensuring that the CPU can operate efficiently without being overwhelmed by interrupt requests. EI enables the processing of interrupts, DI blocks them temporarily, and SIM allows specific configurations of which interrupts should be listened to or ignored, providing programmers with control over what events to respond to.

Examples & Analogies

Think of a telephone system where you can put it on Do Not Disturb (DI), allowing only urgent calls (maskable interrupts) through while keeping the rest silent. The SIM is like programming the phone to only allow calls from specific contacts, ensuring you only receive the messages you want.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Definition of Interrupt: An interrupt is a signal from a peripheral device or software that indicates an event requiring immediate CPU attention.

  • Types of Interrupts: The 8085 supports hardware interrupts (triggered by external signals) and software interrupts (triggered by specific instructions). It further categorizes interrupts as maskable and non-maskable based on whether they can be disabled by software.

  • Interrupt Handling Procedure: When an interrupt occurs, the current instruction completes, the CPU saves its context, and control is transferred to the appropriate ISR. This allows multitasking and error handling without constant checking of devices.

  • Specifics of the 8085 System: The 8085 has various interrupt pins (e.g., TRAP, RST 7.5) with specific priorities and vector addresses. The SIM instruction is important for managing maskable interrupts, controlling which interrupts are active.

  • Terminating the ISR: The process includes executing the ISR, restoring the context, and returning control back to the original program.

  • Understanding these aspects of interrupt handling in the 8085 microprocessor is foundational for programming and creating responsive applications and embedded systems.

Examples & Real-Life Applications

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

Examples

  • A key press generating a hardware interrupt in a computer system.

  • The use of the SIM instruction to enable or disable certain interrupts in a microprocessor program.

Memory Aids

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

🎵 Rhymes Time

  • When the CPU's in the zone, an interrupt must tone, it saves the state and finds the gate, back to work, it will atone.

📖 Fascinating Stories

  • Imagine a waiter (the CPU) in a busy restaurant. Each time a customer (event) raises their hand (interrupt), the waiter finishes serving their current guest (instruction) and promptly attends to the customer who needs help. After resolving the customer's query, the waiter returns to where they left off, maintaining excellent service.

🧠 Other Memory Gems

  • Use ‘SIM’ to Set Interruption Masks; remember, for conditions, it always Acts.

🎯 Super Acronyms

Remember TIMEN

  • TRAP is high priority
  • ISR is routine
  • Maskable can be blocked
  • and Non-maskable is never stopped.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Interrupt

    Definition:

    A signal indicating that an event has occurred which needs the CPU's immediate attention.

  • Term: Interrupt Service Routine (ISR)

    Definition:

    A special function that handles the interrupt when it occurs.

  • Term: Maskable Interrupt

    Definition:

    An interrupt that can be enabled or disabled by the CPU through software.

  • Term: NonMaskable Interrupt (NMI)

    Definition:

    An interrupt that cannot be ignored or disabled via software.

  • Term: SIM Instruction

    Definition:

    An instruction used to manage interrupt masks for enablement and disablement.

  • Term: Vectored Interrupt

    Definition:

    An interrupt where the address of the ISR is determined automatically.

  • Term: NonVectored Interrupt

    Definition:

    An interrupt that does not have a predefined address; the source must be determined by the CPU.