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The microprocessor
system may be measuring
temperatures in the
Sahara desert.
Once a year it receives
a radio signal telling
it to stop measuring
temperatures and send
all last year's data to
base.
This is an INTERRUPT.
The CPU completes it
current instruction.
It then pushes any data
it wishes to save onto
the stack.
It then jumps to a
routine which services
the interrupt.
Once the interrupt
routine is completed, it
pulls the saved data
from the stack and
carries on measuring
temperatures.
There are two pins on
the CPU which, when
taken low, cause a
hardware interrupt.
IRQ can be sensed or
ignored depending the
value of the interrupt
flag in the status
register.
NMI cannot be ignored.
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