PIC16F877A Interrupt Handling Quiz

19 Questions

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

To read keypad data and update the Counter value when a keypad is pressed

Which of the following is an external interrupt source for PIC16F877A?

Keypad input interrupts

What must be set to '1' to enable the RB0/INT external interrupt on PIC16F877A?

INTE

What is the main characteristic of the Timer0 module in PIC16F877A?

It is a readable and writable 8-bit timer/counter

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

It is triggered when the timer reaches its maximum count and overflows

What does the prescaler do in the Timer0 module?

Divides the main clock frequency to reduce the input frequency to Timer0

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?

$rac{1}{(256 * 8,000,000)}$ seconds

What happens when an interrupt is generated in PIC16F877A?

'INTF' is set to '1' and needs to be cleared manually via software

Which component can trigger an interrupt request in PIC16F877A?

'RB0'

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

Allowing the CPU to focus on critical tasks

Which signal change can trigger an external interrupt in PIC16F877A?

State change

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

Setting INTE to '1'

How is the Timer0 module in PIC16F877A described?

8-bit timer/counter with a programmable prescaler

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

Clear INTF via software

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

External interrupts

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

Reading the keypad data and updating the Counter value

Which action generates an interrupt request in PIC16F877A when enabled?

'External interrupts'

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

'GIE' set to '0'

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

Rising edge or falling edge detection

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.

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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