Intel MCS48 User Manual page 287

8216/8226
APPLICATIONS
OF THE
8216/8226
8080
Data Bus
Buffer
The 8080
CPU
Data Bus
is
capable of driving
a single
TTL
load
and
is
more
than adequate
for small, single
board
sys-
tems.
When
expanding
such
a
system
to
more
than
one
board
to increase I/O or
Memory
size,
it is
necessary to provide
a
buffer.
The 8216/8226
is
a
device that
is
exactly fitted to
this
application.
Shown
in
Figure 2
are a pair of
8216/8226 connected
di-
rectly to the
8080
Data Bus and
associated control signals.
The
buffer
is
bi-directional in
nature and
serves to
isolate
the
CPU
data bus.
On
the system
side,
the
DB
lines
interface
with standard
semiconductor
I/O
and
Memory
components and
are
com-
pletely
TTL
compatible.
The
DB
lines
also
provide
a
high
drive capability
(50mA)
so that
an extremely
large
system
can be dirven along
with possible
bus termination networks.
On
the
8080
side the Dl
and
DO
lines are tied
together and
are directly
connected
to
the
8080
Data Bus
for bi-directional
operation.
The
DO
outputs of the
8216/8226
have
a
high
voltage
output
capability of
3.65
volts
which
allows direct
connection
to the
8080 whose
minimum
input voltage
is
3.3
volts.
It
also gives a
very adequate
noise
margin
of
350m V
(worst
case).
The
DIEN
inputs to
8216/8226
is
connected
directly to the
8080.
DIEN
is
tied to
DBIN
so that
proper bus flow
is
maintained,
and CS
is
tied to
BUSEN
so that
the system
side
Data
Bus
will
be
3-stated
when
a
Hold request has been
acknowledged
during
a
DMA
activity.
Memory
and
I/O
Interface to a Bidirectional
Bus
In large
microcomputer
systems
it is
often necessary to
pro-
vide
Memory
and
I/O
with
their
own
buffers
and
at
the
same
time maintain
a direct,
common
interface to
a
bi-directional
Data
Bus.
The 8216/8226
has separated data
in
and data
out
lines
on one
side
and
a
common
bi-directional
set
on
the
other to
accomodate
such
a
function.
Shown
in
Figure 3
is
an
example
of
how
the
8216/8226
is
used
in
this
type
of application.
The
interface to
Memory
is
simple and
direct.
The
memories
used are typically Intel® 8102, 81
02A, 8101
or
8107B-4
and
have
separate data inputs
and
outputs.
The
Dl
and
DO
lines
of the
8216/8226
tie
to
them
directly
and under control of
the
MEMR
signal,
which
is
connected
to the
DIEN
input,
an
interface to the
bi-directional
Data Bus
is
maintained.
The
interface to I/O
is
similar to
Memory. The
I/O devices
used
are typically
Intel
8255s, and can be used
for
both
input
and output
ports.
The
I/O
R
signal
is
connected
di-
rectly
to the
DIEN
input so that proper data flow
from
the
I/O device to the
Data Bus
is
maintained.
The 8216/8226
can be used
in
a
wide
variety
of other
buf-
fering
functions
in
microcomputer
systems such
as
Address
Bus
Drivers,
Drivers to peripheral devices such
as printers,
and
as
Drivers for long length cables to
other peripherals
or
systems.
SYSTEM
DATA
BUS
Figure
2.
8080 Data Bus
Buffer
77
Dl
DO
77
DIEN
I2ICS
8216
8226
(2)
iz
D-i
i7?TR-o BTIn (2)CSO-i
8216
8226
(2)
u
Bl
DIRECTIONAL
DATA
BUS
(8)
Figure
3.
Memory
and
I/O Interface
to a Bidirectional
Bus
7-49