Interrupts are a crucial feature in microcontrollers like the PIC16F887. They allow the microcontroller to respond to external events or internal conditions promptly, without having to continuously poll for them. This improves efficiency and responsiveness in embedded systems.
1- External Interrupts: These interrupts are triggered by external events such as a change in voltage level on a pin, a timer overflow, or a signal from another device. The PIC16F887 has multiple external interrupt pins (e.g., RB0/INT, RB7/INT0) that can be configured to trigger interrupts.
2- Timer Interrupts: The microcontroller's built-in timers can generate interrupts when they overflow or match a specific value. This feature is useful for tasks that require precise timing, such as generating PWM signals or measuring time intervals.
3- Peripheral Interrupts: Some peripherals within the microcontroller, such as the USART (serial communication module) or the ADC (analog-to-digital converter), can generate interrupts to signal the completion of a data transfer or conversion.
When an interrupt occurs, the microcontroller suspends its current execution and jumps to a predefined Interrupt Service Routine (ISR) to handle the interrupt. The ISR performs necessary tasks related to the interrupt, such as reading data from sensors, updating variables, or responding to external commands.
In PIC microcontrollers, interrupts can have different priority levels. This allows the programmer to specify which interrupts should be serviced first if multiple interrupts occur simultaneously. Priority levels can be configured in the microcontroller's interrupt control registers.
To use interrupts in a PIC microcontroller like the PIC16F887, the following steps are typically involved:
4- Clear the interrupt flag in the ISR to acknowledge the interrupt and allow subsequent interrupts of the same type to occur.
list p=16F887 ; list directive to define processor
#include <p16F887.inc> ; processor specific variable definitions
__CONFIG _CONFIG1, _CP_OFF & _CCP1_RB0 & _DEBUG_OFF & _WRT_OFF & _CPD_OFF & _LVP_OFF & _CP_OFF & _BODEN_ON & _MCLRE_ON & _PWRTE_ON & _WDT_OFF & _INTRC_OSC_NOCLKOUT
__CONFIG _CONFIG2, _IESO_OFF & _FCMEN_OFF
; Register definitions
LED_PIN equ RB3 ; Define LED pin
INT_PIN equ RB0 ; Define external interrupt pin
; Interrupt vector
org 0x0004 ; Interrupt vector location
goto ISR ; Jump to ISR when interrupt occurs
; Interrupt Service Routine (ISR)
ISR:
btfss INTCON, INTF ; Check if RB0/INT interrupt flag is set
return ; If not set, return from ISR
; Toggle LED pin
bcf INTCON, INTF ; Clear RB0/INT interrupt flag
movlw 0x01
xorwf LED_PIN, f ; Toggle LED pin
retfie ; Return from interrupt, enable interrupts
; Main program
org 0x0000 ; Program start address
goto Main ; Jump to main program
Main:
bsf STATUS, RP0 ; Bank 1
movlw 0x00
movwf TRISB ; Set PORTB as output
bcf STATUS, RP0 ; Bank 0
bcf INTCON, INTE ; Disable RB0/INT external interrupt
bsf INTCON, INTEDG ; Interrupt on falling edge of RB0/INT
bsf INTCON, GIE ; Enable global interrupts
bcf INTCON, PEIE ; Disable peripheral interrupts
Loop:
nop ; No operation, or other main program instructions
goto Loop ; Endless loop
end ; End of program
+---------------------------------------+
| Start Program |
+---------------------------------------+
| |
| Initialize |
| Configuration |
| Bits |
| |
+---------------------------------------+
| Main Loop |
+---------------------------------------+
| |
| Check for RB0/INT Interrupt |
| |
| ┌───────────────────────┐ |
| │Interruption Déclenchée│ |
| │ (INTF activé) │ |
| └───────────────────────┘ |
| │ |
| ┌─────────┴─────────┐ |
| │ Toggle LED │ |
| └───────────────────┘ |
| │ |
| ┌─────────┴─────────┐ |
| │ Clear INTF Flag │ |
| └───────────────────┘ |
| │ |
| ┌─────────┴─────────┐ |
| │ Return from ISR │ |
| └───────────────────┘ |
| |
+---------------------------------------+
| End Program |
+---------------------------------------+
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