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Tandy 1000 Technical Reference Manual

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Tandy 1000
inter
8259A18259A-218259A-8
Technical Reference Manual
INITIALIZATION COMMAND WORDS 1 AND 2
(ICW1.ICW21
A
s
-A
1S
:
Page starting address
of
service routines. In an
MCS
BO/85
system,
the
8
request
levels
will
generate
CALLs
to
8
locations
equally
spaced
in
memory.
These
can
be
programmed
to
be
spaced
at
intervals
of
4
or
8
memory
locations,
thus
the
8
routines
will
occupy
a
page
of
32
or
64
bytes,
respectively.
The
address
format
is 2
bytes
long
(A
o
-A
1
sl.
When
the
routine
interval
is
4,
A
o
-A
4
are
automatically
inserted
by
the
8259A,
while
As-A
1S
are
programmed
externally.
When
the
routine
interval
is
8,
Ao-A
s
are
automatically
inserted
by
the
8259A,
while
A
6
-A,s
are
programmed
externally.
The
8·byte
interval
will
maintain
compatibility
with
cur·
rent
software,
while
the
4·byte
interval
is
best
for
a ::om·
pact
jump
table.
In an iAPX 86 system
A,s-A"
are inserted in
the
five
most
significant
bits
of
the
vectoring
byte
and
the
8259A sets
the
three
least
significant
bits
according
to
the
interrupt
level. A1Q-AS are
ignored
and ADI (Address interval) has
no effect.
LTlM:
"LTIM=1,
then
the
8259A
will
operate
in
the
level
Interrupt
mode. Edge
detect
logic
on
the
interrupt
inputs
will
be
disabled.
ADI:
CALL
address
interval. ADI = 1
then
Interval
=
4;
ADI = 0 then
interval
=
8.
SNGL: Single. Means
that
this
is
the
only
8259A in
the
system.
"
SNGL
= 1
no
ICW3
will
be
issued.
IC4: "
this
bit
is
set
- ICW4 has
to
be read. " ICW4
Is
not
needed,
set
IC4 =
O.
INITIALIZATION
COMMAND WORD 3 (ICW3)
This
word
is read
only
when
there
is
more
than
one
8259A in
the
system
and
cascading
is used, in
which
case
SNGL
=
O.
It
will
load
the
8·bit slave
register.
The
functions
of
this
register
are:
a.
In
the
master
mode
(either
when
SP =
1,
or
in
buffered
mode
when
M/S =1 in ICW4) a
"1"
is
set
for
each
slave in
the
system.
The
master
then
will
release
byte
1
of
the
call
sequence
(for
MCS·80/85
system)
and
will
enable
the
corresponding
slave
to
release
bytes
2
and 3
(for
iAPX 86
only
byte
2)
through
the
cascade
lines.
b. In
the
slave
mode
(either
when
~
= 0,
or
If
BUF
= 1
and
M/S =0 in ICW4)
bits
2-0
identify
the
slave. The
slave
compares
its
cascade
input
with
these
bits
and,
if
they
are equal,
bytes
2
and
3
of
the
call
sequence
(or
just
byte 2
for
iAPX 86 are released by it
on
the
Data
Bus.
INITIALIZATION
COMMAND WORD 4 (ICW4)
SFNM:
"
SFNM
=1
the
special
fUlly
nested
mode
is
programmed.
BUF:
"BUF
= 1
the
buffered
mode
is
programmed.
In
buffered
mode
SP/EN
becomes
an enable
outpul
and
the
master/slave
determination
is
by
M/S.
MIS:
"buffered
mode
is
selected:
MIS = 1
means
the
8259A Is
programmed
to
be a
master,
MIS = 0
means
the
8259A is
programmed
to
be a slave. "
BUF
=0, MIS
has
no
function.
AEOI:
"AEOI
= 1
the
automatic
end
of
interrupt
mode
is
programmed.
"PM:
Microprocessor
mode:
/LPM
= 0 sets the 8259A
for
MeS-80,
85
system
operation,
/LPM = 1 sets
the
8259A
for
iAPX 86 system
operation.
,.
CASCADE
MODE
Figure
6.
Initialization
Sequence
2-126

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Tandy 1000 Specifications

General IconGeneral
ProcessorIntel 8088
Processor Speed4.77 MHz
RAM128 KB (expandable to 640 KB)
Operating SystemMS-DOS 2.11
ManufacturerTandy Corporation
Release Year1984
StorageSingle or double 5.25" floppy disk drive (360 KB), optional hard drive
SoundTandy 3-voice sound
PortsParallel, Serial
GraphicsCGA (Color Graphics Adapter)
Graphics Modes320x200, 640x200

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