hardware interrupts in 8051 microcontroller
- 1. Module 5: INTERRUPTS PROGRAMMING
- 2. INTERRUPTS Interrupts vs. Polling An interrupt is an external or internal event that interrupts the microcontroller to inform a microcontroller that a device needs its service A single microcontroller can serve several devices by two ways 1) Interrupts • Whenever any device needs its service, the device notifies the microcontroller by sending it an interrupt signal. • Upon receiving an interrupt signal, the microcontroller interrupts whatever it is doing and serves the device. • The program which is associated with the interrupt is called the interrupt service routine (ISR) or interrupt handler. 2) Polling • The microcontroller continuously monitors the status of a given device • When the conditions met, it performs the service • After that, it moves on to monitor the next device until every one is serviced
- 3. Interrupt Method Polling Method Microcontroller time is used efficiently Microcontroller time is not used efficiently Ex: JNB TFx, target Priority can be assigned to the devices Priority cannot be assigned. The devices are served in round robin fashion Microcontroller can enable/disable the interrupts It is not possible in polling method Interrupts vs. Polling
- 4. Six Interrupts in 8051 Six interrupts are allocated as follows • Reset –power-up reset • Two interrupts are set aside for the timers: one for timer 0 and one for timer 1 • Two interrupts are set aside for hardware external interrupts P3.2 and P3.3 are for the external hardware interrupts INT0 (or EX1), and INT1 (or EX2) • Serial communication has a single interrupt that belongs to both receive and transfer(RI and TI)
- 5. Interrupt Service Routine For every interrupt, there must be an interrupt service routine (ISR), or interrupt handler • When an interrupt is invoked, the microcontroller runs the interrupt service routine • For every interrupt, there is a fixed location in memory that holds the address of its ISR • The group of memory locations set aside to hold the addresses of ISR’s is called interrupt vector table
- 7. Steps in Executing an Interrupt Upon activation of an interrupt, the microcontroller goes through the following steps 1.It finishes the instruction it is executing and saves the address of the next instruction (PC) on the stack 2.It also saves the current status of all the interrupts internally (i.e: not on the stack) 3.It jumps to a fixed location in memory, called the interrupt vector table, that holds the address of the ISR 4. The microcontroller gets the address of the ISR from the interrupt vector table and jumps to it • It starts to execute the interrupt service subroutine until it reaches the last instruction of the subroutine which is RETI (return from interrupt) 5.Upon executing the RETI instruction, the microcontroller returns to the place where it was interrupted • First, it gets the program counter (PC) address from the stack by popping the top two bytes of the stack into the PC • Then it starts to execute from that address