Subject Code : Name Of Subject : Microprocessor and assembly language programming Name of Unit : Introduction to Microprossor Topic : Pin function of 8085 Name of Faculty : H.M.Avaiya & Bhargav Halari

25/24/2015Parul Polytechnic Institute H.M.Avaiya

INTRODUCTION Interrupt is a process where an external device can get the attention of the microprocessor. The process starts from the I/O device The process is asynchronous. An interrupt is considered to be an emergency signal that may be serviced. The Microprocessor may respond to it as soon as possible. 35/24/2015Parul Polytechnic Institute H.M.Avaiya

INTRODUCTION What happens when MP is interrupted ? When the Microprocessor receives an interrupt signal, it suspends the currently executing program and jumps to an Interrupt Service Routine (ISR) to respond to the incoming interrupt. Each interrupt will most probably have its own ISR. 45/24/2015Parul Polytechnic Institute H.M.Avaiya

Interrupts in 8085 When the interrupt signal arrives:  The processor will break its routine  Go to a different routine (interrupt service routine)  Complete the interrupt service routine(ISR)  Go back to the “regular” routine 5/24/2015Parul Polytechnic Institute H.M.Avaiya5

Interrupts in 8085 In order to execute an interrupt routine, the processor:  Should be able to accept interrupts (interrupt enable)  Save the last content of the program counter  Know where to go in program memory to execute the ISR  Tell the outside world that it is executing an interrupt  Go back to the saved PC location when finished. 5/24/2015Parul Polytechnic Institute H.M.Avaiya6

Interrupts in 8085 Interrupts increase processor system efficiency by letting I/O device request CPU time only when that device needs immediate attention. An interrupt is a subroutine call initialized by external hardware. The request is asynchronous  it may occur at any point in a program’s execution. 5/24/2015Parul Polytechnic Institute H.M.Avaiya7

8 Interrupts in 8085 Main routine Interrupt Save program counter Disable interrupts Send out interupt acknowledge Service routine INTA Go to service routine Get original program counter Go back EI RET 5/24/2015Parul Polytechnic Institute H.M.Avaiya