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SCHOTTKY BIPOLAR 8216/8226
FUNCTIONAL DESCRIPTION
DB,
DB,
----OOB
O
------oOB
O
'--------1-
----0
cs
OlEN
cs
0
0
Ol~
DB
1 0
OB~
DO
0
1
}HIGH
IMPEDANCE
1
1
01
3
0-------+----1
>--+--..
01,
0-------+---1
"--4--..
DO,
o------t--~
I--~---'
OlEN
~--------
......
003o------t-----c:
1-----+-
......
01
0
0-----
....
"---1---..
OOoo------t-----c:
1-------1-
_ __'
(b) 8226
OlEN
(a)
8216
01
0
0°0
01,
DO,
01
2
0°2
01
3
0°3
Control Gating OlEN,
CS
The
CS
input
is
actually a device select. When it
is
"high"
the
output
drivers are
all
forced
to
their high-impedance
state. When it
is
at
"zero"
the
device
is
selected (enabled)
and
the
direction
of
the
data
flow
is
determined by
the
DIEN input.
The DIEN input controls
the
direction
of
data
flow (see
Figure
1)
for complete
truth
table. This direction control
is
accomplished by forcing
one
of
the
pair
of
buffers into its
high impedance state and allowing
the
other
to
transmit its
data. A simple
two
gate circuit
is
used for this function.
The
8216/8226
is
a device
that
will reduce
component
count
in
mjcrocomputer systems and
at
the
same
time
enhance
noise immunity
to
assure reliable, high performance op-
eration.
Bi-Directional Driver
Each buffered Iine
of
the
four
bit
driver consists
of
two
separate buffers
that
are tri-state
in
nature
to
achieve direct
bus interface and bi-directional capability. On one side
of
thedriver
the
output
of
one buffer and
the
input
of
another
are tied
together
(DB), this side
is
used
to
interface
to
the
system side
components
such
as
memories, I/O, etc., be-
cause its interface
is
direct TTL compatible and it has high
drive (50mA). On
the
other
side
of
the
driver
the
inputs
and
outputs
are separated
to
provide maximum flexibility.
Of·course,
they
can be tied together so
that
the
driver can
be used
to
buffer a
true
bi-directional bus such as
the
8080
Data Bus.
The
DO
outputs
on this side
of
the
driver have a
special high voltage
output
drive capability (3.65V) so
that
direct interface
to
the
8080
and
8008
CPUs
is
achieved with
an
adequate
amount
of
noise immunity (350mV worst case).
Microprocessors like
the
8080
are
MOS
devices and are
generally capable
of
driving a single
TTL
load.
The
same
is
true for
MOS
memory devices. While this
type
of
drive
is
sufficient
in
small systemswith few components, quite often
it
is
necessary
to
buffer
the
microprocessor and memories
when adding
components
or
expanding
to
a multi-board
system.
The
8216/8226
is
a
four
bit bi-directional bus driver specif-
ically designed
to
buffer microcomputersystem components.
Figure 1. 8216/8226 Logic Diagrams
5-164