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Tandy 1000 Technical Reference Manual

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Tandy 1000
Technical Reference Manual
inter
825318253-5
Figure
4.
Block Diagram Showing Control Word
Register and Counter Functions
DATA
BUS
BUFFER
CONTROL
WORD
REGISTER
D,~
Do~~
8253 SYSTEM INTERFACE
The
8253 is a
component
of
the
Intel'·
Microcomputer
Systems
and
interfaces
in
the
same
manner
as all
other
peripherals
of
the
family.
It is
treated
by
the
systems
software
as an
array
of
peripheral
1/0
ports;
three
are
counters
and
the
fourth
is a
control
register
for
MODE
programming
Basically.
the
select
Inputs
AO.
A 1
connect
to
the
AO.
A 1
address
bus
signals
of
the
CPU
n,e
CS
can be
derrved
directly
from
the
address
bus uSing a
linear
select
method
Or
it can be
connected
to
the
output
of
a
decoder.
such
as
an
Intel-
8205
for
larger
systems
Control Word Aegllter
The
Control
Word
Register
is
selected
when
AD,
A 1
are
11
It
then
accepts
information
from
the
data
bus
buller
and
stores
it
in
a
register.
The
information
stored
in
this
register
controls
the
operational
MODE
of
each
counter,
selection
of
binary
or
BCD
counting
and
the
loading
of
each
count
register
The
Control
Word
Register
can
only
be
written
Into.
no
read
operation
of
its
contents
is
available
Counter
#0,
Counter #1, Counter
#2
These
three
functional
blocks
are
Identical
in
operation
so
only
a
single
Counter
will
be
described.
Each
Counter
consists
of
a
single.
16-blt.
pre-sellable,
DOWN
counter
The
counter
can
operate
in
either
binary
or
BCD
and
its
input.
gate
and
output
are
configured
by
the
selectIOn
of
MODES
stored
In
the
Control
Word
Register
The
counters
are
fully
independent
and
each
can
have
separate
Mode
configuration
and
counting
operation
binary
or
BCD.
Also.
there
are
special features
In
the
control
word
that
handle
the
loading
of
the
count
value
so
that
software
overhead
can
be
minimized
for
these
functions
The
reading
of
the
contents
of
each
counter
is
available
to
the
programmer
with
simple
READ
operations
for
event
counting
applications
and
special
commands
and
logic
are
included
in
the
8253 so
that
the
contents
of
each
counter
can
be
read
"on
the
fly"
Without
having
to
Inhibit
the
clock
Input
Figure
5.
8253 SYlitem Interface
6-141
AFN-00745C

Table of Contents

Other manuals for Tandy 1000

Preview: User Guide
User Guide337 pages
Preview: Programmer's Reference Guide
Programmer's Reference Guide251 pages
Preview: Basic Reference Manual
Basic Reference Manual411 pages
Preview: Owner's Manual
Owner's Manual46 pages

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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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