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Introduction to Interrupts
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Today, we’ll learn about interrupts in microprocessors. Can anyone tell me what an interrupt is?
An interrupt is a signal that tells the CPU to stop current work and execute a different task.
Exactly! It allows the CPU to handle events efficiently. Why do you think we use interrupts instead of polling all the time?
Because polling takes more time and resources. Interrupts are faster.
Great point! Interrupts enable event-driven processing, which is crucial for multitasking!
What types of interrupts are there?
We can categorize them as hardware and software interrupts, along with maskable and non-maskable types. Remember the acronym HSMN for this classification!
HSMN - Hardware, Software, Maskable, Non-Maskable! Got it!
Excellent! Let's summarize: Interrupts help CPUs respond to important events without constant checking.
Types and Purpose of Interrupts
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Now, let's dive deeper into the types of interrupts. Can someone explain the difference between maskable and non-maskable interrupts?
Maskable interrupts can be turned off by the CPU, but non-maskable interrupts can't be disabled.
Correct! Non-maskable interrupts are often used for critical tasks. Can you provide an example of each?
An example of a maskable interrupt could be a keyboard input, while a non-maskable interrupt might be a power failure signal.
Exactly! Understanding these distinctions helps manage how CPUs respond to various events. Let’s look at the flow of the interrupt process.
What steps are involved in this flow?
The steps are: interrupt occurs, finish current instruction, save the context, execute the ISR, restore context, and return to the main program. Let's remember this as 'F-S-R-E-R-R'!
F-S-R-E-R-R for the flow! That makes it easier to remember!
Interrupt Handling in the 8085 Microprocessor
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Now, let's focus on the 8085 microprocessor and its interrupt management. How many hardware interrupt pins does the 8085 have?
It has five hardware interrupt pins!
Correct! Which of these has the highest priority?
TRAP is the highest priority interrupt!
Great! What about RST 7.5? How is it handled in the system?
RST 7.5 is a maskable, vectored interrupt. It jumps to a fixed address.
Exactly! And how do we enable it using software?
Using the SIM instruction, where we set the appropriate bits in the accumulator to control the interrupts.
Correct! Remember, 'SIM' controls interrupts, like a 'Switch Interruption Mechanism'.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section explains the fundamentals of interrupt mechanisms in microprocessors, detailing how the 8085 microprocessor manages interrupts like RST 7.5. It covers types of interrupts, the interrupt process flow, and specific instructions for controlling interrupts, with a practical focus on configuring a system for event-driven processing.
Detailed
Detailed Summary of Interrupt Handling and Timer Interfacing (RST 7.5)
This section focuses on the concept of interrupt handling in microprocessors, particularly in the 8085 architecture. An interrupt is defined as a signal from a peripheral device that prompts the microprocessor to halt its current task and execute an Interrupt Service Routine (ISR) to address the event. The significance of interrupts lies in facilitating event-driven processing, allowing for multitasking and efficient error handling without the need for constant polling of devices.
Types of Interrupts
The section details various types of interrupts, including:
• Hardware Interrupts - Triggered by external signals.
• Software Interrupts - Triggered by program instructions like RST.
• Maskable Interrupts - Can be enabled or disabled by software.
• Non-Maskable Interrupts (NMI) - Critical interrupts that cannot be disabled.
• Vectored/Non-Vectored Interrupts - Differentiates based on how the ISR is accessed by the CPU.
Interrupt Process Flow
The flow of handling interrupts is outlined step-by-step to illustrate how a CPU responds, starting from the occurrence of the interrupt to executing the ISR and restoring context.
1. Interrupt occurs.
2. Current instruction completion.
3. Context saving.
4. Vectoring to ISR.
5. ISR execution.
6. Context restoration.
7. Return to the interrupted program.
8085 Interrupts
The 8085 microprocessor manages five hardware interrupts, focusing on RST 7.5, which is a vectored, maskable interrupt. It explains how to utilize SIM and RIM instructions to control interrupt handling, including resetting pending interrupts and setting interrupt masks using the accumulator's bit format.
Conclusion
Understanding how the 8085 microprocessor handles interrupts, particularly RST 7.5, is vital for designing systems that require efficient event-driven architectures. This foundational knowledge is beneficial for interfacing peripherals and utilizing programmable timers like the 8253/8254 for robust control over timing events.
Audio Book
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Overview of Interrupts in 8085 Microprocessor
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The 8085 has 5 hardware interrupt pins and can also handle software interrupts.
Detailed Explanation
The 8085 microprocessor is equipped with five hardware interrupt pins that allow it to respond to external signals. These include TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. Additionally, the 8085 can execute software interrupts through specific instructions labeled RST n.
Examples & Analogies
Think of these interrupt pins as emergency buttons in a factory. When an unexpected situation arises, pressing any of these buttons (interrupts) alerts the main control system (the CPU) to pause its current work and address this new priority task.
Types of Hardware Interrupts
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- TRAP (Non-Maskable, Vectored)... 5. INTR (Maskable, Non-Vectored).
Detailed Explanation
Interrupts in the 8085 are classified into various types:
1. TRAP is a non-maskable and vectored interrupt, meaning it cannot be ignored or disabled, prioritizing critical events.
2. RST 7.5, RST 6.5, and RST 5.5 are maskable interrupts, which can be programmed to be ignored by the system when necessary.
3. INTR is a maskable, non-vectored interrupt, waiting for an external signal to provide its interrupt address. This allows developers to manage the system's response to various scenarios effectively.
Examples & Analogies
Imagine a classroom where students can raise hands to ask questions. The teacher (CPU) will respond to raised hands (interrupts). However, if a student raises their hand very urgently (TRAP), the teacher must address that student first, ignoring any other hands. In contrast, if students can lower their hands at any time (maskable interrupts), the teacher can choose to respond to others if needed.
Controlling Maskable Interrupts
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● EI (Enable Interrupts): Enables the INTR interrupt... ● SIM (Set Interrupt Mask) Instruction.
Detailed Explanation
To manage interrupts effectively, the 8085 provides several instructions:
- EI (Enable Interrupts) is used to allow the CPU to receive interrupt requests.
- DI (Disable Interrupts) stops the CPU from responding to maskable interrupts.
- SIM (Set Interrupt Mask) configures which maskable interrupts can be serviced. The SIM instruction uses bits in the accumulator to specify which interrupts to enable or disable.
Examples & Analogies
Think of a traffic light system. When it's green, cars (interrupt requests) can pass (be processed), but when it's red (DI), no cars can move through. The traffic management system (SIM) can also control which routes (interrupts) are open or closed depending on the situation.
Interrupt Process Flow
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- Interrupt Occurs: A hardware signal... 6. Context Restoration: The saved CPU state is popped from the stack.
Detailed Explanation
The flow of handling an interrupt in the 8085 begins with the occurrence of an interrupt signal. Following this signal, the CPU completes its current instruction, saves its state (context), identifies the required ISR (Interrupt Service Routine) address, executes it, restores the previous state, and resumes the previous task. This systematic approach ensures smooth processing without event loss.
Examples & Analogies
Consider a chef in a busy kitchen. When an urgent order comes in (interrupt), the chef finishes the current dish (current instruction), writes down notes about the dish process (context), goes to prepare the urgent dish (ISR), and once completed, returns to finishing the previous dish. This allows the chef to handle multiple tasks without confusion.
Programming and Using RST 7.5
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The RST 7.5 instruction is a maskable interrupt... The data in the Accumulator before executing SIM defines the mask for these interrupts.
Detailed Explanation
RST 7.5 is a key instruction for interrupt handling, which directs the CPU to a specific memory address upon an interrupt event. It's maskable, meaning a programmer can decide when it should be acknowledged or ignored using the SIM instruction. The format of the accumulator during SIM helps set these conditions effectively.
Examples & Analogies
Imagine an assistant who handles mail for a busy office. The assistant (RST 7.5) knows where to take each piece of mail (interrupt event) when it comes and can choose to ignore or attend to it based on the office manager's (programmer's) instruction whether they are busy elsewhere. The manager's directive (SIM) helps manage what takes priority.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Interrupt: A mechanism to alert the CPU for immediate attention.
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ISR: The routine executed to handle an interrupt.
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RST 7.5: A specific interrupt in the 8085 that is maskable and vectored.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Using RST 7.5 to toggle an LED connected to the 8085 through an integrated 8255 PPI.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Interrupts call like a bell, when events occur, they ring the bell.
📖 Fascinating Stories
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Imagine a busy CPU like a waiter in a restaurant; interrupts are diners waving to get their attention.
🧠 Other Memory Gems
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HSMN - Remember Hardware, Software, Maskable, Non-Maskable to categorize interrupts.
🎯 Super Acronyms
F-S-R-E-R-R - Flow of interrupt
- Finish
- Save
- Rest
- Execute
- Restore
- Return.
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 that an event has occurred, prompting it to halt its current operations to execute an ISR.
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Term: ISR (Interrupt Service Routine)
Definition:
A special routine executed when an interrupt occurs, to address the specific event that caused the interrupt.
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Term: Maskable Interrupts
Definition:
Interrupts that can be enabled or disabled by the programmer.
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Term: NonMaskable Interrupts
Definition:
Critical interrupts that cannot be turned off and require immediate attention.
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Term: SIM (Set Interrupt Mask)
Definition:
An instruction used in the 8085 microprocessor to control maskable interrupts.
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Term: RIM (Read Interrupt Mask)
Definition:
An instruction that reads the current state of interrupt masks and pending interrupts into the accumulator.