
Interrupts
specific ISR it is used to run a polling program to check
the status of the peripheral flags in turn. On finding a
flag set high the program will be directed to the relevant
ISR.
In terms of software, this polling procedure is no differ-
ent from that described previously. The difference, and
it is a very important one, is that it doesn't run continu-
ously but is only called when an interrupt request is
received. There is no need whatever for the computer to
keep on checking the peripherals. Figure 4.4 shows a
hypothetical situation where interrupts from the three
peripherals of Figure 4.3 arrive quite randomly and are
dealt with