Question

when using microcontroller 8051 How do you think are other interrupts processed while running the interrupt handler?

Answer 1

8051 Microcontroller has two levels of Interrupt priority:

• high
• low

Multiple interrupts can be handled by assigning priorities. They are set by bit in IP at byte address B8H and it is bit addressable. A 1-bit in bit position indicates high priority and a 0-bit indicates low priority.

In case of multiple interrupts,

• If two interrupt occur at same time then the interrupt with more priority executes first. If priority of both the interrupt are same, interrupt with high polling order executes first.
• If a high priority interrupt arrives while a low priority interrupt is running, the handler will be interrupted and the high priority handler will run. When high priority handler executes 'RETI', low priority handler resumes and when this handler executes 'RETI' control is passed to main program.
• No other source can interrupt while a high priority interrupt is running even the source is a high priority interrupt with high in polling order.
• A low priority interrupt handler is invoked only if no other interrupt is running. A low priority interrupt cannot preempt another low priority interrupt with high polling order.