List of
Contents
Page
INTRODUCTION . ... ...... ...... .... .... ....... ........ ........ ........... 1
DESCRIPTION ............................................................... 3
General ............................................................................ 3
Interrupt Sequence ......................................................... 4
Interrupt Masking ........................................................... 5
PROGRAMMING CONSIDERATIONS ...................... 5
General ............................................................................ 5
Initialization Command Words ..................................... 6
Operational Command Words ....................................... 8
List of
Illustrations
Figure
Interrupt
Controller
block
diagram ............................... 1
INTRODUCTION
The
Intel 8259A
Programmable
Interrupt
Controller
(PIC)
forms
the
interface
between
the
devices capable of
generating
interrupt
requests
and
the
interrupt
control
line
of
the
8086 processor (CPU
on
the
System Board).
Interrupt
requests
are supplied
to
the
PIC,
when
the
device requires
an
associated service
routine
to
be
undertaken.
The
PIC
functions
as
the
manager
of
the
interrupt
driven
processing
system;
generating
an
active
interrupt
to
the
8086 processor
only
when
an
incoming
interrupt
request
has
a
higher
priority
than
any
interrupt
service
routine
already
in
operation.
On
acknowledgement
from
the
CPU
that
it
is able
to
accept
the
generated
interrupt,
the
PIC
supplies vectoring
data
to
the
CPU
which
acts as a
pointer
to
the
required service
routine.
The
vectoring data,
the
mode
of
operation
of
the
PIC
and
the
priority of
the
interrupt
requests
are
set
up
by software
within
the
Boot
PROM
and
BIOS.
To Next Page
Loading...
