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Introduction to Interrupts
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Welcome, class! Today, we're diving into interrupts within the 8085 microprocessor. Can anyone tell me what an interrupt is?
Isn't it a signal to the CPU to stop its current task and execute something else?
Exactly! An interrupt is a signal indicating that an event needs immediate attention. What do you think is the purpose of having interrupts?
To save CPU time by not constantly checking for events?
Great point! This allows for event-driven processing, where the CPU can manage multiple tasks efficiently.
What are the different types of interrupts?
Good question! We have hardware interrupts, software interrupts, maskable and non-maskable interrupts. Let’s remember it with the acronym 'HSMN' – Hardware, Software, Maskable, Non-Maskable. It highlights the crucial differences.
To summarize, interrupts allow efficient CPU handling of events and support multitasking, enhancing system responsiveness.
Types of Interrupts
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Let’s discuss each type of interrupt in detail. Starting with hardware interrupts, can anyone give an example?
Like when I press a key on the keyboard?
Exactly! Now, what about software interrupts?
Those are triggered by specific instructions like 'RST' in assembly programming.
Very good! Now, does anyone know the difference between maskable and non-maskable interrupts?
Maskable interrupts can be ignored by the CPU, while non-maskable interrupts cannot. They are used for critical events.
Correct! Remember, non-maskable interrupts are crucial and cannot be disabled by the system.
In summary, hardware interrupts come from devices, and software interrupts come from code, with maskable interrupts being manageable by the CPU.
Managing Interrupts with SIM and RIM
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Now that we know about interrupts, let’s explore how to manage them. The SIM instruction is used for controlling interrupts. Can someone explain its purpose?
SIM is used to enable or disable maskable interrupts, right?
Exactly! And what about RIM? How does it fit in?
RIM reads the state of maskable interrupts and pending interrupts into the accumulator.
Spot on! These two instructions are essential for seamless interrupt handling in our programs.
So, to recap, SIM controls the status of maskable interrupts while RIM checks their status. It’s all about cooperation between managing and monitoring interrupts effectively in our programs.
Practical Implementation Example
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Let's dive into a practical example. We will explore how to toggle an LED using RST 7.5. Why do you think interrupts are necessary for this task?
They allow us to respond immediately to the RST 7.5 signal to change the LED's state.
Correct! In our code, we start by configuring the 8255 to set up the LED as an output. What do we need next?
We need to enable the RST 7.5 interrupt using the SIM instruction.
Right! Then we define the ISR, where we’ll read the current state of the LED and toggle it. Can anyone summarize the flow of this implementation?
First, configure the LED, then enable interrupts with SIM, and finally define and implement the ISR.
Excellent recap! Remember, hardware interrupts provide dynamic interactivity in our systems.
Introduction & Overview
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Quick Overview
Standard
The section discusses the fundamental concepts of interrupts in the 8085 microprocessor, including the types of interrupts (hardware, software, maskable, non-maskable), their handling processes, and the management of specific interrupt sources through the SIM and RIM instructions. It highlights critical components like interrupt priority, interrupt service routines, and practical programming examples relevant to both interrupt handling and timer interfacing.
Detailed
Detailed Summary of Interrupt Handling in 8085 Microprocessor
The 8085 microprocessor manages interrupts to ensure efficient processing of events, allowing the CPU to respond promptly to external signals or software requests. An interrupt is a mechanism that disrupts the current execution flow of the program, prompting the CPU to execute a specific task referred to as the Interrupt Service Routine (ISR).
Purpose of Interrupts:
- Event-Driven Processing: Facilitates quick responses to external events without the need to continuously poll devices.
- Multitasking: Permits the system to manage multiple operations or tasks concurrently.
- Error Handling: Assists in managing critical errors effectively.
Types of Interrupts:
- Hardware Interrupts: Triggered by external hardware devices (e.g., keyboard, timers).
- Software Interrupts: Triggered by specific software instruction, such as the RST and INT instructions.
- Maskable Interrupts: Can be enabled or disabled through software.
- Non-Maskable Interrupts (NMI): Critical interrupts that cannot be ignored.
- Vectoring: The process of directing the CPU to the appropriate ISR address upon occurrence of an interrupt.
This section also details the functions and operational instructions for managing interrupts, including how the SIM instruction is used to control maskable interrupts. Additionally, it includes practical assembly code examples demonstrating the implementation of interrupt handling and configuring the 8254/8253 timer to showcase time-delayed functionalities.
Audio Book
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Overview of Interrupts in 8085
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The 8085 has 5 hardware interrupt pins and can also handle software interrupts.
Detailed Explanation
The 8085 microprocessor can handle both hardware and software interrupts, which plays a critical role in how it interacts with external devices and responds to events. Hardware interrupts are signals coming from external devices, while software interrupts are triggered by specific instructions within a program.
Examples & Analogies
Think of the 8085 microprocessor like a busy office worker. The hardware interrupts are like phone calls from clients seeking immediate assistance, while software interrupts are like reminders put in the worker’s calendar to do specific tasks. Just as the worker must manage these interruptions efficiently without losing track of ongoing work, the microprocessor must also manage interrupts to respond promptly to various events.
Hardware Interrupt Pins and Their Priorities
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8085 Hardware Interrupt Pins (from highest to lowest priority):
1. TRAP (Non-Maskable, Vectored): Edge and level triggered. Highest priority. Jumps to fixed address 0024H. Cannot be disabled by software.
2. RST 7.5 (Maskable, Vectored): Edge triggered (positive going edge). Jumps to fixed address 003CH. Can be masked by the SIM instruction.
3. RST 6.5 (Maskable, Vectored): Level triggered. Jumps to fixed address 0034H. Can be masked by the SIM instruction.
4. RST 5.5 (Maskable, Vectored): Level triggered. Jumps to fixed address 002CH. Can be masked by the SIM instruction.
5. INTR (Maskable, Non-Vectored): Level triggered. Requires external hardware to provide the vector address. Jumps to the address corresponding to the RST n instruction. Can be masked by EI/DI instructions.
Detailed Explanation
The 8085 microprocessor includes five dedicated interrupt pins that allow it to interact with hardware devices. Each interrupt has a priority level, with TRAP being the highest priority, meaning it must be processed first. The maskable interrupts (RST 7.5, RST 6.5, RST 5.5) can be enabled or disabled using specific instructions, allowing for flexible control over which interrupts are active, while the INTR is a non-vectored interrupt that requires external help to know which interrupt service routine to execute.
Examples & Analogies
Imagine a fire alarm system within a building. The TRAP interrupt is like the fire alarm that goes off irrespective of what people are doing inside the building; it must be dealt with immediately. The other interrupts are like other alarms that can be turned off if they're not needed—like a smoke detector that can be disabled if there’s no smoke. The INTR is akin to a notification from the maintenance team, which requires extra steps to acknowledge before acting.
Controlling Maskable Interrupts
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Controlling Maskable Interrupts:
● EI (Enable Interrupts): Enables the INTR interrupt and allows RST 7.5, 6.5, and 5.5 to be processed if their individual masks are clear.
● DI (Disable Interrupts): Disables the INTR interrupt and prevents further maskable interrupts from being processed.
● SIM (Set Interrupt Mask) Instruction: This instruction is crucial for controlling the RST 7.5, RST 6.5, and RST 5.5 interrupts.
Detailed Explanation
To manage how interrupts are processed, the 8085 microprocessor uses three key instructions: EI to enable interrupts, DI to disable them, and SIM to set specific masks for individual interrupts. By masking interrupts, the microprocessor can temporarily ignore certain signals, allowing the program to run without interruptions until it’s ready to handle them.
Examples & Analogies
Think of controlling interrupts like managing a TV remote. When you press the 'Mute' button (DI), you're blocking out any sounds in the room (disabling interrupts). Pressing the 'Volume Up' button (EI) allows sound to come back in as soon as you’re ready. You might also use 'Channel Up' or 'Channel Down' buttons (SIM) to select which channels you want to listen to, thereby customizing what notifications you receive based on your preferences.
SIM Instruction Format
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Accumulator Format for SIM Instruction:
D7 D6 D5 D4 D3 D2 D1 D0
SOD SDE X R7.5 MSE M7.5 M6.5 M5.5
- D7 (SOD): Serial Output Data. Data to be sent out on the SOD pin.
- D6 (SDE): Serial Data Enable. If 1, enables SOD function. If 0, SOD pin is tristated.
- D5 (X): Don't care.
- D4 (R7.5): Reset RST 7.5 flip-flop. If 1, clears the RST 7.5 pending interrupt.
- D3 (MSE): Mask Set Enable. If 1, the mask bits are loaded from the Accumulator into the interrupt mask register.
- D2 (M7.5): Mask for RST 7.5. If 1, RST 7.5 is masked (disabled).
- D1 (M6.5): Mask for RST 6.5. If 1, RST 6.5 is masked.
- D0 (M5.5): Mask for RST 5.5. If 1, RST 5.5 is masked.
Detailed Explanation
The SIM instruction format is structured in an accumulator with specific bits defined for different functionalities like serial output data and the control of maskable interrupts. For example, setting the flip-flop for RST 7.5 to ensure it clears any pending interrupt helps in proper handling of repeated interrupts without conflicts.
Examples & Analogies
Think of the SIM instruction as controlling different features in a smart home system. Each bit in the instruction allows you to toggle different devices: some may activate lights (SOD), others may enable security alerts (SDE), and some determine if you want certain alerts to be silenced (mask). Just like you pick what functionalities to enable in your smart home, the SIM instruction allows the programmer to control how interrupts are managed.
Returning from ISR
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An RET instruction is typically used at the end of an 8085 ISR. If nested interrupts are possible or if the ISR needs to re-enable interrupts early, EI followed by RET might be used.
Detailed Explanation
At the end of an Interrupt Service Routine (ISR), the processor uses the RET instruction to return control to the main program. If there’s a chance of nested interrupts—meaning another interrupt might occur before the current ISR is completed—the EI instruction can be used to enable interrupts before finishing the current ISR, ensuring that new events can still be handled on time.
Examples & Analogies
Once a fire drill is over and everyone is accounted for (the ISR), the fire officer gives a final report and tells people they can go back to their regular activities (RET). However, if an emergency were to arise while the drill was happening, the officer should also inform people quickly about that (EI), ensuring everyone is ready to respond to any new developments.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Interrupt: A signal that interrupts the current program flow to execute an ISR.
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ISR: A routine executed in response to an interrupt.
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SIM Instruction: Instruction for managing maskable interrupts.
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RIM Instruction: Instruction for reading the interrupt status.
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Types of Interrupts: Hardware and software, maskable, and non-maskable interrupts.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Using the RST 7.5 interrupt to toggle an LED.
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Configuring the 8255 to respond to interrupts.
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Implementing an ISR that alters the state of an output device.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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When signals arise, interrupts make their call, / CPU must respond to avoid a fall.
📖 Fascinating Stories
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Imagine a courier delivering important messages to a busy office worker. The courier's urgent knock is the interrupt, prompting the worker to pause their tasks and address the message.
🧠 Other Memory Gems
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Remember SIM for 'Set Interrupt Masks', it's the key to managing interrupts for the CPU.
🎯 Super Acronyms
HSMN - for Hardware, Software, Maskable, Non-Maskable interrupts.
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 CPU indicating an event that requires immediate attention.
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Term: ISR (Interrupt Service Routine)
Definition:
A special routine executed when an interrupt occurs.
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Term: SIM (Set Interrupt Mask)
Definition:
An instruction used to control maskable interrupts.
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Term: RIM (Read Interrupt Mask)
Definition:
An instruction that reads the status of interrupts into the accumulator.
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Term: Hardware Interrupt
Definition:
Interrupts triggered by external hardware events.
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Term: Software Interrupt
Definition:
Interrupts triggered by executing a specific instruction in the program.
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Term: Maskable Interrupt
Definition:
Interrupts that can be enabled or disabled by the CPU.
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Term: NonMaskable Interrupt (NMI)
Definition:
Critical interrupts that cannot be ignored by the CPU.