4- External & internal Interrupts

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4- External & internal Interrupts Powered By Docstoc
					External & internal Interrupts
Interrupt Sources
• There are 21 different interrupts and each     one has its own vector
    located in a predefined location at the start of the memory space.

• 3 external interrupts  (INT0, INT1 and INT2) are available at pins
    PD2(pin 16) and PD3 (pin 17) and PB2 (pin 3). They are Edge or
    Level triggered interrupts (except Int2 which is only edge

•    Reset input (pin 9) which causes also an interrupt and can be
    both externally and internally initiated.

• If enabled, the interrupts will trigger even if the INT0 and INT1
    pins are configured as outputs. This feature provides a way of
    generating a software interrupt (how?).

• INT0, INT1 (level) and INT2 are detected asynchronously       (no
    Clock needed and thus they can be used to get the µC from sleep
    Reset and Interrupt Vectors
Vector Program   Source Interrupt   Definition
No.    Address
1       $000     RESET External     Reset
                 Pin, Power-on
                 Reset, Brown-out
                 Reset, Watchdog
                 Reset, and JTAG
2      $002       INT0              External Interrupt Request 0
3      $004      INT1               External Interrupt Request 1
4      $006      TIMER2 COMP        Timer-Counter2 Compare Match
5      $008      TIMER2 OVF         Timer-Counter2 Overflow
6      $00A      TIMER1 CAPT        Timer-Counter1 Capture Event
7      $00C      TIMER1 COMPA       Timer-Counter1 Compare Match A
8      $00E      TIMER1 COMPB       Timer-Counter1 Compare Match B
9      $010      TIMER1 OVF         Timer-Counter1 Overflow
Vecto   Program Source Interrupt   Definition
r No.   Address
10      $012     TIMER0 OVF        Timer-Counter0 Overflow

11      $014     SPI, STC          Serial Transfer Complete

12      $016     USART, RXC        USART, Rx Complete

13      $018     USART, UDRE       USART Data Register Empty

14      $01A     USART, TXC        USART, Tx Complete

15      $01C     ADC ADC           Conversion Complete

16      $01E     EE_RDY            EEPROM Ready

17      $020     ANA_COMP          Analog Comparator

18      $022     TWI               Two-wire Serial Interface

19      $024     INT2 External     Interrupt Request 2

20      $026     TIMER0 COMP       Timer-Counter0 Compare Match

21      $028     SPM_RDY           Store Program Memory Ready
Notes to interrupt vector table

•   If the program never enables an interrupt source, the Interrupt
    Vectors are not used, and regular program code can be placed at
    these locations.
External Interrupts:
 • To enable INT0/INT1/INT2:
     The I-bit in the Status Register must be set. But also the
     corresponding External Interrupt Request Enable bit in the General
     Interrupt Control Register (GICR)

 •   When an event on the INT0/INT1/INT2 pin triggers an interrupt
     request, INT0-Flag/INT1-Flag/INT2-Flag (bit 6/7/5 of the General
     Interrupt Flag Register – GIFR) becomes set. The flag is cleared
     when the interrupt routine is executed. Alternatively, the flag can
     be cleared by writing a logical one to it.

                          General Interrupt Flag
Interrupt Triggering

 The external interrupts INT0/INT1 can be triggered by a falling or
 rising edge or a low level.

The external interrupts INT2 can only be triggered by a falling
  or rising edge.
ISC2 (interrupt sense control of INT2):
        ISC2 = 0 -> Falling Edge
        ISC2 = 1 -> Rising Edge

                   MCU Control and Status Register
Using Interrupts in C

The access to the AVR interrupt system is implemented with the
                                  interrupt keyword.
interrupt [2] void external_int0(void)
    /* Place your code here */

interrupt [10] void timer0_overflow(void)
    /* Place your code here */
Using Interrupts in C (Contd.)

•Interrupt vector numbers start with 1.
•The compiler will automatically save the affected registers when calling
the interrupt functions and restore them back on exit.
•a RETI assembly instruction is placed at the end of the interrupt
•Interrupt functions can't return a value nor have parameters.
•You must also set the corresponding bits in the peripheral control
registers to configure the interrupt system and enable the interrupts.
Using the CodeVisionAVR Wizard by interrupts
 Including Assembly Lines in the Program

You can include assembly language anywhere in your program using the #asm
and #endasm directives.

void delay(unsigned char i)
   while (i--)
       /* Assembly language code sequence */

Inline assembly may also be used.
   #asm("sei") /* enable interrupts */

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Description: This slides explain the concept of interrupts and sources of interrupt in ATmega16 microcontroller and how to program them