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Interactive Audio Lesson
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Introduction to Interrupts
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Let's start by understanding what interrupts are. Can anyone tell me their significance in microprocessor-based systems?
Interrupts allow the CPU to pause its current task to handle important events, right?
Yes, exactly! They enable event-driven processing, which is crucial for efficient CPU usage. What about the difference between hardware and software interrupts?
Hardware interrupts come from external devices, while software interrupts are generated by program instructions.
That's correct! Remember the acronym 'HS' for Hardware and Software to keep them distinct. Now, let's summarize: interrupts allow for efficient CPU utilization by responding to external or internal signals.
Handling RST 7.5 in 8085
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Now that we understand interrupts, let's dive into RST 7.5 on the 8085. Who can explain how we configure it?
We need to set up the 8255 to output to an LED and then write an ISR starting at the vector address 003CH.
And we must remember to use the SIM instruction to enable the interrupt!
Exactly! The SIM instruction is crucial. It can reset pending interrupts and allow for selecting which interrupts to mask. Let’s summarize: setup involves configuring the I/O and writing the ISR where the LED toggling occurs.
Timer Interfacing
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Moving forward, let's explore timer interfacing with the 8254. What are some key features of this timer?
It has three independent 16-bit counters and can generate precise timing signals.
It can be programmed for different modes, like generating square waves or delays!
Great observations! Remember the modes: Mode 0 is for one-shot delays, while Mode 3 generates a square wave. Let's summarize the importance of understanding these timers in embedded systems.
Introduction & Overview
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Quick Overview
Standard
In this section, we explore two programs related to interrupt handling using RST 7.5 and timer interfacing using the 8254 timer. The details cover the structure of assembly language code, expected outcomes, and the significance of each component used in hardware interfacing with microprocessors.
Detailed
Overview of Programs to be Executed
This section highlights the practical implementations required for understanding microcontroller operations, particularly focusing on interrupts and timer usage.
Programs on Interrupt Handling
The first program demonstrates how to configure the 8085 microprocessor to respond to hardware interrupts using the RST 7.5 signal. It enables students to observe interactive behavior, specifically toggling an LED through an interrupt service routine (ISR). The program consists of initialization, interrupt enabling, and the ISR to handle LED toggling, with specific memory instructions mapped out. The outcomes yield direct observations of how interrupts facilitate real-time processing and event handling.
Timer Interfacing Programs
The second program illustrates interfacing with the 8254 Programmable Interval Timer to generate controlled delays and square waves. By configuring the timer to operate in different modes (such as Mode 0 for one-shot pulsing and Mode 3 for continuous square wave generation), students will gain practical experience observing LED states and understanding timer functionality. The assembly code outlines control word configurations and execution strategies to achieve desired temporal outputs, fostering a deeper grasp of lower-level programming in real-time systems.
In summary, this section not only provides hands-on programming experiences but also contextualizes their relevance in hardware design and embedded systems.
Audio Book
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Part A: Interrupt Handling (8085)
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Assume 8085 I/O addresses for 8255 (Port A=80H, CWR=83H) and 8254 (Counter 0=90H, CWR=93H).
Program A.1: Toggle LED via RST 7.5 Interrupt
Objective: To configure an 8085 system such that an RST 7.5 hardware interrupt toggles the state of an LED connected to 8255 Port A, bit 0.
Assumption: LED connected to 8255 Port A, bit 0 (PA0). 8255 Port A configured as output.
Control Word for 8255 (Port A = Output):
- D7=1 (I/O Mode), D6,D5=00 (Mode 0), D4=0 (PA=Out), D3=1 (PCU=In), D2=0 (Mode 0), D1=1 (PB=In), D0=1 (PCL=In)
- Resulting Control Word: 10001111b = 8FH
Assembly Code:
; Main Program - Configures 8255, Enables Interrupts ; Starting Address: 2000H ORG 2000H START: MVI A, 8FH ; Configure 8255: Port A as Output OUT 83H ; Write to 8255 CWR MVI A, 00H ; Initialize LED to OFF (PA0 = 0) OUT 80H ; Output to Port A MVI A, 18H ; Enable RST 7.5 interrupt (SIM byte: D4=1 to reset pending, D3=1 for MSE, D2=0 to unmask 7.5) SIM ; Set Interrupt Mask EI ; Enable Global Interrupts LOOP: JMP LOOP ; Infinite loop, waiting for interrupt ; --- Interrupt Service Routine (ISR) for RST 7.5 --- ; This routine is automatically called when RST 7.5 occurs. ORG 003CH ; ISR should ideally be placed here ISR_RST7_5: PUSH PSW ; Save Accumulator and Flag Register PUSH B ; Save BC pair (if used) PUSH D ; Save DE pair (if used) PUSH H ; Save HL pair (if used) IN 80H ; Read current state of Port A into Accumulator XRI 01H ; Toggle bit 0 (00000001b). If PA0 was 0, it becomes 1; if 1, it becomes 0. OUT 80H ; Output the new state back to Port A MVI A, 18H ; Re-enable RST 7.5 by resetting its pending flip-flop SIM ; (D4=1 for R7.5, D3=1 for MSE, D2=0 for M7.5) POP H ; Restore HL pair POP D ; Restore DE pair POP B ; Restore BC pair POP PSW ; Restore Accumulator and Flag Register EI ; Re-enable global interrupts before returning (important for nested interrupts) RET ; Return from Interrupt to the main program
Memory Layout (Example, depends on trainer kit's initial memory state):
- Main Program (Starting at 2000H):
| Address | Hex Code | Instruction / Operand |
| :------ | :------- | :-------------------- |
| 2000H | 3E | MVI A |
| 2001H | 8F | (Operand) |
| 2002H | D3 | OUT |
| 2003H | 83 | (Operand) |
| 2004H | 3E | MVI A |
| 2005H | 00 | (Operand) |
| 2006H | D3 | OUT |
| 2007H | 80 | (Operand) |
| 2008H | 3E | MVI A |
| 2009H | 18 | (Operand) |
| 200AH | 30 | SIM |
| 200BH | FB | EI |
| 200CH | C3 | JMP |
| 200DH | 0C | (Operand - LSB) |
| 200EH | 20 | (Operand - MSB) |
- ISR (Starting at 003CH):
| Address | Hex Code | Instruction / Operand |
| :------ | :------- | :-------------------- |
| 003CH | F5 | PUSH PSW |
| 003DH | C5 | PUSH B |
| 003EH | D5 | PUSH D |
| 003FH | E5 | PUSH H |
| 0040H | DB | IN |
| 0041H | 80 | (Operand) |
| 0042H | EE | XRI |
| 0043H | 01 | (Operand) |
| 0044H | D3 | OUT |
| 0045H | 80 | (Operand) |
| 0046H | 3E | MVI A |
| 0047H | 18 | (Operand) |
| 0048H | 30 | SIM |
| 0049H | E1 | POP H |
| 004AH | D1 | POP D |
| 004BH | C1 | POP B |
| 004CH | F1 | POP PSW |
| 004DH | FB | EI |
| 004EH | C9 | RET |
Expected Outcomes:
- Initially, the LED connected to PA0 will be OFF.
- Upon pressing the RST 7.5 button, the LED should turn ON.
- Upon pressing the RST 7.5 button again, the LED should turn OFF.
- This toggling behavior should continue with each subsequent interrupt.
Detailed Explanation
In this part of the program, we configure the 8085 to handle an RST 7.5 interrupt. The goal is to make an LED connected to the microprocessor toggle its state every time the interrupt occurs. The program first sets up the 8255 to connect the LED as an output. It then enables the RST 7.5 interrupt by configuring the interrupt mask and eventually loops waiting for that interrupt. Upon the interrupt activation, the ISR is executed, which toggles the LED's state before returning control back to the main program.
Examples & Analogies
Think of this process like a light switch where every time a doorbell rings (the interrupt), instead of getting up to manually turn on the light, the switch (the microprocessor) automatically toggles the light on or off. The ISR can be imagined as the trained butler who responds instantly to the doorbell.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Interrupts enable CPUs to efficiently manage multiple tasks by responding to events.
-
RST 7.5 is a specific interrupt in the 8085 processor architecture for handling high-priority tasks.
-
The 8254 timer can operate in multiple modes for various timing applications.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
Using RST 7.5 to toggle an LED demonstrates the interrupt's practical application.
-
Programming the 8254 to create a square wave illustrates its flexibility in generating precise timing signals.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
-
Interrupts aid the CPU's plan, pausing work to lend a hand!
📖 Fascinating Stories
-
Imagine a postman (the interrupt) that interrupts a chef (the CPU) to deliver an urgent message (the event). The chef quickly checks and resumes cooking!
🧠 Other Memory Gems
-
Remember the acronym RISE: RST 7.5 Interrupts Support Events!
🎯 Super Acronyms
Use HATS for handling interrupts
- Hardware
- Active
- Timer
- Software.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Interrupt
Definition:
A signal that temporarily halts the current execution of a program to manage events requiring immediate attention.
-
Term: RST 7.5
Definition:
A maskable hardware interrupt in the 8085 microprocessor that triggers an ISR.
-
Term: ISR (Interrupt Service Routine)
Definition:
A special block of code that handle interrupt requests when an interrupt is acknowledged.
-
Term: 8254 Timer
Definition:
A programmable interval timer capable of generating precise time delays and square wave outputs.