Interrupt In 8051

Interrupt is one of the powerfull concept in microcontroller.

• If interrupt occurs in microcontroller,then controller completes the execution of the current instruction and starts the execution of an Interrupt Service Routine (ISR).
• ISR is a piece of code that tells the controller what to do & when the interrupt occurs.
• After the execution of ISR, controller returns back to the instruction.

Types Of Interrupt

• Two type of interrupt
  1.Hardware interrupt.
  2.Software interrupt.

Hardware interrupt.

• If the interrupts are generated by the interfaced devices like switch is called hardware interrupt.

Software interrupt.

• Interrupts are generated by a piece of code is called software interrupt.

• 8051 has six interrupts of which five are available to the programmer.
  1.RESET interrupt
  2.Timer interrupts
  3.External interrupts
  4.Serial interrupt

Reset Interrupt

• This is known as Power on Reset .
• If RESET interrupt is received, the controller restarts executing code from 0000H location.
• This is an interrupt which is not available to programmer.

Timer Interrupt

• A timer interrupt notifies the microcontroller that the corresponding Timer has finished counting.

External Interrupt

• There are two external interrupts to serve external devices. INT0 – P3.2 , INT1 – P3.3.
• An external interrupt notifies the microcontroller that an external device needs its service.

Serial Interrupt

• Interrupt is used for serial communication.
• It notifies the controller whether a byte has been received or transmitted.

Interrupt Programming

• Configuring the Interrupt Enable (IE) register.
• IE is used to enable or disable the various available interrupts.

Interrupt Enable Register

• T o enable any interrupt EA must be set to 1.
• ET0,ET1,ET2 are used to enable timer interrupt.
• EX0,EX1 are used to enable external interrupt.
• ES are used to enable Serial interrupt.
• EA- EA bit acts as a lock bit.
• EA bit is not set, the interrupt will not function.

External Interrupt Programming

• External interrupt can be edge triggered or level triggered.
  1.Edge triggering.
  Interrupt is enabled for a high to low transition at INTx pin.
  2.Level triggering
  Interrupt is enabled for a low at INTx pin.
• The edge or level trigger is decided by the TCON register. The TCON register has following bits:
• The IT0 and IT1 bits make the external interrupt 0 and 1.
  If 0=level triggering.
  If 1=edge triggering.

Code

 #include <REGX51.H>
 unsigned char count;
 void main(void)
 {
 IE=0x81; // Enable hardware interrupt
 TCON=0x01;
 while(1)
 {
 P1=count;
 }
 }
 // interrupt function
 void extint0() interrupt 0
 {
  count=count+1;
 }