Interrupts
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The document discusses interrupts for the 8085 microprocessor. It defines an interrupt as a signal sent by an external device to request that the processor perform a particular task. When an interrupt occurs, the processor suspends the current program and jumps to an interrupt service routine (ISR) corresponding to that interrupt. Interrupts can be hardware interrupts, caused by signals on processor pins, or software interrupts, caused by specific instructions. The 8085 has 5 hardware interrupts of varying priority levels - TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. It also has 8 software interrupts from RST 0 to RST 7. Each interrupt type has unique characteristics regarding priority
Interrupts
- 2. INTERRUPTS Interrupt is signals send by an external device to the processor, to request the processor to perform a particular task or work. Mainly in the microprocessor based system the interrupts are used for data transfer between the peripheral and the microprocessor. The processor will check the interrupts always at the 2nd T-state of last machine cycle.
- 3. . •What happens when MicroProcessor is interrupted? • If there is any interrupt it accept the interrupt and send the INTA (active low) signal to the peripheral. •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. The vectored address of particular interrupt is stored in program counter. •Each interrupt will most probably have its own ISR.
- 4. RESPONDING TO INTERRUPTS Responding to an interrupt may be immediate or delayed depending on whether the interrupt is maskable or non-maskable and whether interrupts are being masked or not. There are two ways of redirecting the execution to the ISR depending on whether the interrupt is vectored or non-vectored. Vectored: The address of the subroutine is already known to the Microprocessor Non Vectored: The device will have to supply the address of the subroutine to the Microprocessor
- 5. TYPES OF INTERRUPTS HARDWARE INTERRUPTS Here Microproceessor pins(peripheral devices ) are used to receive interrupt requests. SOFTWARE INTERRUPTS Cause of the interrupt is an execution of Instruction.
- 6. HARDWARE INTERRUPTS 8085 has 5 hardware Interrupts Trap RST 7.5 RST 6.5 RST 5.5 INTR
- 7. TRAP It is a non-maskable interrupt. It is unaffected by any mask or interrupt enable. TRAP has the highest priority and vectored interrupt. In sudden power failure, it executes a ISR and send the data from main memory to backup memory. There are two ways to clear TRAP interrupt. 1.By resetting microprocessor (External signal) 2.By giving a high TRAP ACKNOWLEDGE (Internal signal)
- 8. RST 7.5 The RST 7.5 interrupt is a maskable interrupt. It has the second highest priority. It is edge sensitive. ie. Input goes to high and no need to maintain high state until it recognized. It is a Maskable interrupt. It is disabled by, 1.DI instruction 2.System or processor reset. 3.After reorganization of interrupt.
- 9. RST 6.5 and 5.5: The RST 6.5 and RST 5.5 both are level triggered. . ie. Input goes to high and stay high until it recognized. Maskable interrupt. It is disabled by, 1.DI, SIM instruction 2.System or processor reset. 3.After reorganization of interrupt. Enabled by EI instruction. The RST 6.5 has the third priority whereas RST 5.5 has the fourth priority.
- 10. INTR INTR is a maskable interrupt. It is disabled by, 1.DI, SIM instruction 2.System or processor reset. 3.After reorganization of interrupt. Enabled by EI instruction. Non- vectored interrupt. After receiving INTA (active low) signal, it has to supply the address of ISR. It has lowest priority. It is a level sensitive interrupts. ie. Input goes to high and it is necessary to maintain high state until it recognized
- 11. SOFTWARE INTERRUPTS The software interrupts are program instructions. These instructions are inserted at desired locations in a program. The 8085 has eight software interrupts from RST 0 to RST 7. The vector address for these interrupts can be calculated as follows. Interrupt number * 8 = vector address For RST 5,5 * 8 = 40 = 28H Vector address for interrupt RST 5 is 0028H
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