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Tandy 1000 Technical Reference Manual

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Tandy 1000
inter
825318253·5
Technical Reference Manual
FUNCTIONAL DESCRIPTION
General
The
8253 is a
programmable
interval
timer/counter
specifically
designed
for
use
with
the
Intel'·
Micro-
computer
systems. Its
function
is
that
of
a
general
purpose,
multi-timing
element
that
can be
treated
as an
array
of
I/O
ports
in
the
system
software.
The 8253 solves
one
of
the
most
common
problems
in
any
microcomputer
system,
the
generation
of
accurate
time
delays
under
software
control.
Instead
of
setting up
timing
loops
In
systems
software,
the
programmer
configures
the
8253
to
match
his
requirements,
initializes
one
of
the
counters
of
the
8253
with
the
desired
quantity.
then
upon
command
the
8253
will
count
out
the
delay and
interrupt
the
CPU
when
it
has
completed
its tasks.
It
is easy to see
that
the
software
overhead
is
minimal
and
that
multiple
delays
can
easily be
maintained
by
assignment
of
Priority
levels
Other
counter/timer
functions
that are
non-delay
in
nature
but
als0
common
to
most
microcomputers
can be
implemented
with
the
8253
•
Programmable
Rate
Generator
• Event
Counter
•
Binary
Rate
Multiplier
• Real
Time
Clock
•
Digital
One-Shot
•
Complex
Motor
Controller
Data
Bus
Buffer
This
3-state,
bi-directional,
8-bit
buffer
is used
to
interface
the
8253
to
the
system
data
bus. Data is
transmitted
or
received
by
the
buffer
upon
execution
of
INput
or
OUTput
CPU
instructions.
The
Data
Bus
Buffer
has
three
basic
functions.
1
Programming
the
MODES
of
the
8253
2
Loading
the
count
registers
3
Reading
the
count
values
Read/Write
Logic
The
Read/Write
Logic
accepts
inputs
from
the
system
bus
and
in
turn
generates
control
signals
for
overall
deVice
operation
It is
enabled
or
disabled
by
CS
so
that
no
operation
can
occur
to
change
the
function
unless
the
device
has been
selected
by
the
system
logic
RO
(Read)
A
"low"
on
thiS
Input
Informs
the 8253
that
the
CPU
IS
inpuWng
data In
the
form
of
a
counters
value
WR{Write)
A
"low"
on
thiS
Input
,nforms
the 8253 that
the
CPU
IS
outputting
data in the
form
of
mode
Informatron
or
loading
counters
AO,A1
These
inputs
are
normally
connected
to
the
address
bus.
Their
function
is
to
select
one
of
the
three
counters
to
be
operated
on
and
to
address
the
control
word
register
for
mode
selection.
CS
(Chip
Select)
A
"low"
on
this
input
enables
the
8253
No
reading
or
writing
will
occur
unless
the
device
is selected.
The
CS
input
has
no
effect
upon
the
actual
operation
of
the
counters
INTERNAL
BUS
/
Figure
3.
Block
Diagram
Showing
Data
Bus
Buffer
and
Read/Write
Logic
Functions
--
------~
CS
RD
WR
A,
Ao
0
1
0 0 0
Load Counter No. 0
0
1
0 0 1
Load Counter No. 1
0
~
0
1
0
Load Counter
No.2
0
1
0
1 1
Write Mode Word
0 0 1 0 0
Read
Counter No. 0
0 0
1 0
1
Read
Counter
No.1
--
-----
--~-
0
0
1
1
0
Read
Counter
NO.2
0
0
1
1 1
No-Operation 3-State
1
X
X
X X
Disable 3-State
0
1
1
X
X
No-Operation 3-State
6-140
AFN-Q074SC

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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