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Interactive Audio Lesson
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Introduction to Interrupt Handling
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Today, we're going to explore the concept of interrupt handling in microprocessors. Can anyone tell me why interrupts are important?
Interrupts help the microprocessor manage events without constantly checking each device.
Exactly! Interrupts allow for efficient event-driven processing. Can anyone name the two types of interrupts?
Hardware interrupts and software interrupts!
Correct! Remember the acronym HSI—Hardware, Software, Interrupts. Let's also consider context saving; why is it necessary during an interrupt?
It’s needed to preserve the state of the program that was interrupted.
Right! This preservation allows the program to resume seamlessly. Let’s summarize: Interrupts enable efficient interaction with external events—HSI is the key acronym here.
Examining the Procedure for Interrupt Handling
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Now that we understand interrupts, let’s go through the setup. Who can describe the first step for Part A of the experiment?
We need to identify the RST 7.5 input pin on the 8085 trainer kit.
Correct! Then we connect an LED to the output pin of the 8255 PPI, which will help us visualize our interrupt actions. What do we do next?
We enter the main program starting from a memory location, like 2000H, and configure 8255 for output.
Perfect! The outline for this procedure is very structured. A good memory aid is ‘Setup, Program, Observe—SPO.’ Let's reflect on how we execute the ISR and its role.
Timer Interfacing with 8254
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Let's shift gears to Part B: Timer interfacing with the 8254. What is the first setup step here?
Identifying the 8254 PPI on the trainer kit and locating its CLK, GATE, and OUT pins.
Absolutely! Then what should we connect the OUT pin to for observation?
We connect it to an LED for delay observation or to an oscilloscope to view the square wave.
Excellently put! After that, we must calculate the initial count for our timer based on the desired delay. Who remembers the formula for that?
Initial Count = Delay * Clock Frequency!
Great! It's crucial to manage expected delays vs. clock frequency to ensure accuracy. Let’s summarize this with ‘SETUP Linkage, Count Control—SLCC.’
Executing and Observing Timer Functions
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We’ve configured the 8254; now let’s review the execution process. If we run our delay program, what should we observe?
The LED should change state after the set delay!
Exactly! And for square wave generation, how do we ensure continuous output?
Keep the GATE pin high for counting.
Spot on! Remember to document what you observe post-execution. Use CAH—Count, Analyze, and Highlight as your memory aid for this step.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section details the step-by-step procedure for performing the experiment, which is divided into two parts: Interrupt Handling using the 8085 microprocessor and Timer Interfacing using the 8254 timer. It includes system setups, program entries, execution, and observations necessary for proper execution.
Detailed
Detailed Summary of Procedure
Overview
This section describes the detailed procedure to execute Experiment No. 5, focusing on Interrupt Handling and Timer Interfacing using 8085/8086 microprocessors and the 8253/8254 Programmable Interval Timer.
Experiment Structure
The experiment is structured into two main parts:
1. Part A: Interrupt Handling (8085) - This involves setting up an 8085 microprocessor to handle interrupts and observe their operation by toggling an LED connected through a Programmable Peripheral Interface (8255).
2. Part B: Timer Interfacing (8254) - This section covers configuring the 8254 timer to generate specific time delays and square waves and observing the output.
Each part involves systematic procedures: setting up the system, programming necessary instructions, and executing the program while observing the output to validate the functionality. This hands-on approach enhances the understanding of hardware interrupts, subroutine calling in ISRs, and timer functionalities.
Audio Book
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Part A: Interrupt Handling (8085)
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- System Setup:
- Identify the RST 7.5 input pin or dedicated push button on your 8085 trainer kit.
- Connect an LED (with a suitable current limiting resistor) to one of the output pins of an integrated 8255 PPI (e.g., Port A, bit 0). Ensure the 8255 is configured for output initially.
- Program Entry:
- Enter the main program (including 8255 initialization and interrupt enable) starting from a suitable memory location (e.g., 2000H).
- Enter the Interrupt Service Routine (ISR) for RST 7.5 starting at its vector address, which is 003CH. If your kit's monitor prevents writing directly to 003CH, you may need to write the ISR elsewhere and put a JMP instruction at 003CH pointing to your ISR. However, ideally, the ISR is written directly at 003CH.
- Execution and Observation:
- Run the main program (GO 2000).
- The LED connected to the 8255 output port should initially be in a specific state (e.g., OFF).
- Press the RST 7.5 push button or apply a positive edge signal to the RST 7.5 pin.
- Observe the LED toggling its state (e.g., from OFF to ON). Each subsequent press should toggle the LED again.
- Observe the Program Counter and register contents (if your kit allows real-time observation or single-stepping through ISR).
Detailed Explanation
In this part, we set up the necessary environment to handle hardware interrupts using the 8085 microprocessor. The system setup involves identifying the RST 7.5 pin used for interrupts and connecting an LED for visual feedback. The program entry involves writing a main program that initializes the system and specifies the ISR for handling the interrupt. When an interrupt occurs (such as pressing the RST 7.5 button), we expect the LED to toggle its state, demonstrating the interrupt functionality. The observations made during execution help confirm that the system reacts correctly to the interrupt signal.
Examples & Analogies
Imagine you're a waiter in a restaurant (the microprocessor) who is busy serving food (running the main program). If a customer presses the bell on the table (the interrupt), you stop what you're doing, take care of that customer's need (execute the ISR), and once that's done, you go back to serving food where you left off. Connecting an LED is like putting up a sign for the customers to see whenever you serve them, enhancing their dining experience.
Part B: Timer Interfacing (8254)
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- System Setup:
- Identify the 8254 PPI on your trainer kit. Locate its CLK, GATE, and OUT pins for one of the counters (e.g., Counter 0).
- Connect the OUT0 pin to an LED (for delay observation) or directly to an oscilloscope (for square wave observation).
- Ensure an appropriate clock source is provided to CLK0 (many kits provide an internal clock, or you may need to connect an external crystal/oscillator output). For square wave generation, a stable clock input is essential.
- Program Entry:
- Calculate the required initial count based on the desired delay or frequency (refer to "Calculation of Initial Count" in the Theory section).
- Enter the assembly programs for Mode 0 and Mode 3 starting from a suitable memory location (e.g., 2000H for each).
- Execution and Observation (Mode 0 - Delay):
- Run the Mode 0 program (GO 2000).
- Observe the LED: It should remain in its initial state for the programmed delay duration and then change state once (e.g., from OFF to ON) indicating the terminal count was reached. This is a one-shot delay.
- Execution and Observation (Mode 3 - Square Wave):
- Run the Mode 3 program (GO 2000).
- Connect the OUT0 pin to an oscilloscope.
- Observe the generated waveform on the oscilloscope. Verify its frequency and duty cycle against your calculations.
Detailed Explanation
In Part B, we are interfacing the 8254 timer to generate specific time delays and square wave outputs. We first set up the timer by connecting its control pins to visualize output. The configuration is crucial; we need to determine the correct initial count based on our timing requirements. There are two modes of operation demonstrated here: Mode 0 for generating a single time delay and Mode 3 for creating a continuous square wave. By closely observing the LED or using an oscilloscope, we can confirm the timer's performance and accuracy based on our calculations.
Examples & Analogies
Think of a bakery with a timer (the 8254) that signals when cookies need to come out of the oven. When the timer is set (configured), it starts counting down (entering the initial count). Once the time is up (the delay), the timer rings (the LED turns ON), indicating that the cookies should be checked. In another scenario, if the bakery wants to keep the kitchen busy, the timer can be set to repeatedly ding every few minutes (square wave mode), reminding bakers to check on items consistently, ensuring they never miss a batch.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Interrupts allow the microprocessor to react to external events efficiently.
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The ISR temporarily replaces the main program execution to handle the interrupt.
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8255 PPI facilitates peripheral connections with the microprocessor.
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The 8254 timer is essential for generating precise delays and timing signals.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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When pressing a key on a keyboard, a hardware interrupt signals the CPU to read the key input.
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Using the 8254 timer to generate a square wave can be seen in clock generation for synchronous circuits.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Interrupts come to play, events can't delay; they signal the CPU, so work's on the way.
📖 Fascinating Stories
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Imagine a mailman (ISR) who runs to deliver urgent mail (interrupt) while the office (main program) continues working. The mailman returns after delivering, resuming their tasks.
🧠 Other Memory Gems
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Remember HSI for types of interrupts: Hardware, Software, Interrupts.
🎯 Super Acronyms
Use SLCC
- **S**ETUP
- **L**inkage
- **C**ount **C**ontrol for timer interfacing steps.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Interrupt
Definition:
A signal to the microprocessor from a peripheral device or software indicating an event requiring immediate attention.
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Term: ISR
Definition:
Interrupt Service Routine; a special routine that the microprocessor executes in response to an interrupt.
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Term: 8255 PPI
Definition:
Programmable Peripheral Interface; allows for connecting the microprocessor to a variety of peripherals.
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Term: 8254 Timer
Definition:
A Programmable Interval Timer used to generate specific time delays and square waves.
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Term: SIM Instruction
Definition:
Set Interrupt Mask; used in 8085 to control maskable interrupts.