8086 Interrupt Priority and ISR: Quiz and Flashcards

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Questions and Answers

What is the purpose of the IRET instruction in an ISR?

To return from an interrupt and restore the old values of flags, CS, and IP (correct)

To disable all interrupts

To jump to the next interrupt

To call the next interrupt handler

What is the type of interrupt generated when a divisor is larger than the specified destination?

Type 0 interrupt (correct)

Type 1 interrupt

Type 2 interrupt

Type 4 interrupt

Which of the following instructions is used to debug a program by executing it one instruction at a time?

HLT

Single Step (correct)

WAIT

INTO

How are the 8086 interrupts divided into groups?

Into five groups: reset, external hardware, nonmaskable, software, and internal Signup and view all the answers

What is the purpose of the HLT instruction?

To initiate idle states and suspend operation Signup and view all the answers

What happens if an interrupt of higher priority occurs while a lower priority interrupt is being serviced?

The lower priority interrupt is terminated and the higher priority interrupt is serviced Signup and view all the answers

Which flag is set to enable the single step operation?

TF Signup and view all the answers

What is the purpose of the reset mechanism in the 8086 processor?

To terminate all operations and set the IP and CS to 0x0000 Signup and view all the answers

What is the interrupt priority order in the 8086 processor?

Reset, internal, exceptions, software, nonmaskable, external Signup and view all the answers

What is the purpose of the WAIT instruction?

To check the logic level of the TEST input prior to going to idle state Signup and view all the answers

What is the purpose of the INTR interrupt?

To handle external hardware interrupts Signup and view all the answers

What is the interrupt vector for the INTO instruction?

0010H Signup and view all the answers

What type of interrupt is not affected by the Interrupt Enable Flag (IF) bit in the Status Register?

Non-maskable interrupt Signup and view all the answers

Which instruction is used to enable the external interrupt request (INTR)?

STI Signup and view all the answers

What is the maximum number of software interrupts supported by the 8086?

256 Signup and view all the answers

How does the CPU handle the INTR input during the execution of an ISR?

The CPU clears the IF bit to prevent other signals on the INTR pin Signup and view all the answers

What is the priority of software interrupts compared to external interrupts?

Software interrupts have a higher priority than external interrupts Signup and view all the answers

What is the trigger mechanism for the NMI input?

Positive edge-triggered Signup and view all the answers

Study Notes

Internal Interrupts

Divide Error: occurs when a division operation results in a quotient that is larger than the specified destination, triggering a Type 0 interrupt.
Interrupt on Overflow (INTO): causes a Type 4 interrupt when an overflow occurs during an arithmetic operation.

Single Step

Used for debugging purposes
Program is executed one instruction at a time
TF flag is set to enable single step operation, causing a Type 1 interrupt

Breakpoint

Causes execution to stop at a specific location
Used for debugging purposes

HLT and Wait Instructions

HLT: suspends processor operation and initiates idle state
Wait: checks the logic level of the TEST input prior to going to idle state, resumes execution when TEST input becomes zero

Interrupt Service Routine (ISR)

Ends with the IRET instruction, which pops old flags, CS, and IP from the stack
IRET must be used at the end of each ISR

8086 Interrupts Classification

Divided into five groups: Reset, External Hardware Interrupt, Nonmaskable Interrupt, Software Interrupts, and Internal Interrupts

Interrupt Priority

Priority order: Reset, Internal Interrupts & Exceptions, Software Interrupts, Nonmaskable Interrupts, and External Interrupts
Higher priority interrupts can interrupt lower priority ISR

External Hardware Interrupts

RESET: initializes and resets the CPU
INTR: controlled by the Interrupt Enable Flag (IF) bit, can be masked or unmasked
NMI: non-maskable, positive edge-triggered, and must be active for two consecutive clock cycles

External Hardware Interrupt Instructions

CLI: disables external interrupt requests (INTR)
STI: enables external interrupt requests (INTR)

Software Interrupt Instruction

INT n: initiates a software interrupt, supports up to 256 interrupts, and has a higher priority than external interrupts

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Description

This quiz covers the basics of interrupts in 8086 microprocessors, including interrupt service routines, return from interrupt instructions, and types of interrupts. It also explores the different groups of interrupts, including reset, external hardware, non-maskable, software, and internal interrupts.