PIC16F877A Interrupt Handling Quiz
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Questions and Answers

What is the main purpose of using interrupts in embedded systems?

  • To display the Counter value on an LCD screen
  • To update the Counter value every second
  • To read keypad data and update the Counter value when a keypad is pressed (correct)
  • To generate a delay between operations
  • Which of the following is an external interrupt source for PIC16F877A?

  • Display interrupts
  • Keypad input interrupts (correct)
  • Communication interrupts
  • Clock cycle interrupts
  • What must be set to '1' to enable the RB0/INT external interrupt on PIC16F877A?

  • INTE (correct)
  • RB0
  • GIE
  • INTF
  • What is the main characteristic of the Timer0 module in PIC16F877A?

    <p>It is a readable and writable 8-bit timer/counter</p> Signup and view all the answers

    Which of the following statements about Timer0 Overflow Interrupt is correct?

    <p>It is triggered when the timer reaches its maximum count and overflows</p> Signup and view all the answers

    What does the prescaler do in the Timer0 module?

    <p>Divides the main clock frequency to reduce the input frequency to Timer0</p> Signup and view all the answers

    How would you calculate the delay period produced by Timer0 in PIC16F877A with a prescaler value of 256 and a clock frequency of 8 MHz?

    <p>$rac{1}{(256 * 8,000,000)}$ seconds</p> Signup and view all the answers

    What happens when an interrupt is generated in PIC16F877A?

    <p>'INTF' is set to '1' and needs to be cleared manually via software</p> Signup and view all the answers

    Which component can trigger an interrupt request in PIC16F877A?

    <p>'RB0'</p> Signup and view all the answers

    What is the main benefit of using interrupts in embedded systems?

    <p>Allowing the CPU to focus on critical tasks</p> Signup and view all the answers

    Which signal change can trigger an external interrupt in PIC16F877A?

    <p>State change</p> Signup and view all the answers

    What is required to enable the RB0/INT external interrupt in PIC16F877A?

    <p>Setting INTE to '1'</p> Signup and view all the answers

    How is the Timer0 module in PIC16F877A described?

    <p>8-bit timer/counter with a programmable prescaler</p> Signup and view all the answers

    What should be done to manually clear INTF after an interrupt is generated on PIC16F877A?

    <p>Clear INTF via software</p> Signup and view all the answers

    Which interrupt source in PIC16F877A requires both INTE and GIE to be set to '1' for enabling?

    <p>External interrupts</p> Signup and view all the answers

    What is the role of the ISR in handling interrupts in embedded systems?

    <p>Reading the keypad data and updating the Counter value</p> Signup and view all the answers

    Which action generates an interrupt request in PIC16F877A when enabled?

    <p>'External interrupts'</p> Signup and view all the answers

    What must be done to disable all unmasked interrupts on PIC16F877A?

    <p>'GIE' set to '0'</p> Signup and view all the answers

    Which type of interrupt changes RB0/INT state for detection on PIC16F877A?

    <p>Rising edge or falling edge detection</p> Signup and view all the answers

    Study Notes

    Calculating Delay Period using Overflows

    • The period of the timer overflow (𝑇𝑜𝑣𝑒𝑟𝑓𝑙𝑜𝑤) is approximately 8.192 ms.
    • The formula to calculate the delay period using overflows is 𝐹𝑂𝑆𝐶 𝐹𝑜𝑣𝑒𝑟𝑓𝑙𝑜𝑤 = 4 × 𝑝𝑟𝑒𝑠𝑐𝑎𝑙𝑒𝑟 × max 𝑐𝑜𝑢𝑛𝑡.
    • For a 1-second delay at 1:32 prescaler, approximately 122 overflows are needed.

    Interrupt Handling in PIC16F877A

    • The PIC16F877A has a single interrupt vector (00004H) that points to a single address in memory to handle interrupts.
    • An Interrupt Service Routine (ISR) function must be written to handle the RB0/INT external and/or Timer0 overflow interrupt.
    • The ISR function disables all unmasked interrupts, checks the interrupt flags, clears the interrupt flags, and re-enables interrupts.

    Timer0 Overflow Interrupt

    • Timer0 overflow occurs when the counter reaches its terminal count and overflows, resetting the counter.
    • To enable the Timer0 overflow interrupt, both TMR0IE and GIE must be set to ‘1’.
    • When an interrupt is generated, TMR0IF is set to ‘1’ by the MCU and must be cleared manually via software.

    Interrupt Sources in PIC16F877A

    • External interrupts
    • Overflow/underflow interrupts
    • A/D conversion interrupts
    • Communication interrupts

    RB0/INT External Interrupt

    • An external interrupt source is a signal sent to the MCU from an I/O device or another MCU.
    • To enable the RB0/INT external interrupt, both INTE and GIE must be set to ‘1’.
    • When an interrupt is generated, INTF is set to ‘1’ by the MCU and must be cleared manually via software.

    Timer0 Module

    • The Timer0 module is a readable and writable 8-bit timer/counter.
    • It has a programmable prescaler and can be powered using the internal clock cycle and external clock.
    • If enabled, it can generate an interrupt upon overflow.

    Enabling/Disabling Interrupts

    • Every interrupt source has an enable bit in a configuration register.
    • Interrupt disabling is also called interrupt masking.
    • GIE is used to disable all unmasked interrupts temporarily.

    Interrupt Service Routine (ISR)

    • ISR should be as short as possible to prevent data corruption and interrupt overlapping.
    • ISR must clear the interrupt flag and re-enable interrupts.

    Using Interrupts in Embedded Systems

    • Interrupts make systems efficient and responsive to critical events.
    • Interrupts make code easier to manage.
    • However, interrupts can be confusing and error-prone if not regulated properly.

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    Description

    Test your knowledge on PIC16F877A interrupt handling including overflow periods, interrupt service routine, and interrupt vector. Learn about writing an ISR function to handle RB0/INT external and/or Timer0 overflow interrupt.

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