A note on interrupts - page 3

Here is a WIZ sequence which monitors a wire which pulses high every once in a while. Each time we get a pulse we toggle the state of an LED. The wire is connected to a WIZ register called "wire-reg".

   wire-reg => X
   LED => not => LED
   (0) => repeat if zero

The first instruction will wait indefinitely until the wire goes high. As it waits, no power is consumed and no other WIZ on the chip is affected.

When the wire goes high and wire-reg becomes ready, the sequence proceeds and toggles the LED. (Here assume "not" is a device which inverts a 0/1 input).

This is a classic "interrupt handler". The pulse happens, the "handler" executes, it does whatever it does, then goes back to "sleep". Instead of "bringing in" some subroutine when the trigger occurs, here we simply have that subroutine "always running", but sitting in a zero-power wait state, blocked until the trigger allows it to proceed.

No other programs are "interrupted" because there are no other programs here. Of course, other programs in other WIZes are totally running, but that has nothing to do with *this* WIZ.