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SCHOTTKY BIPOLAR
8205
FUNCTIONAL DESCRIPTION
Decoder
The
8205
contains a one
out
of
eight binary decoder. It
ac-
ceptsa three bit binary code and by gating this input, creates
an exclusive
output
that
represents
the
value
of
the
input
code.
For
example, if a binary code
of
101 was present on
the
AO,
A1 and A2 address input lines, and
the
device was enabled,
an active low signal would appear on
the
05
output
line.
Note
that
all
of
the
other
output
pins are sitting
at
a logic
high,
thus
the
decoded
output
is
said
to
be exclusive.
The
decoders
outputs
will follow
the
truth
table shown below
in
the
same manner for
all
other
input
variations.
Enable
Gate
When using a decoder it
is
often necessary
to
gate
the
out-
puts with timing
or
enabling signals so
that
the
exclusive
output
of
the
decoded value
is
synchronous with
the
overall
system.
The
8205
has a
bu
itt-in function for such gating.
The
three
enable inputs
(E
1, E2, E3) are ANDed together and create
a single enable signal for
the
decoder.
The
combination
of
both active
"high"
and active
"Iow"
device enable inputs
provides
the
designer with a powerfully flexible gating func-
tion
to
help reduce package
count
in
his system.
~
I""
.
l-
I""
.
I-.
I""
....
-
DECODER
-
....
l-
I""
-
....
.......
....
ENABLE
GATE
--
_"I
"'
(E'i·"E2·E3)
.!......I
ADDRESS
ENABLE
OUTPUTS
A
o
A,
A
2
E,
E
2
E
3
0 1 2
3
4
5
6
7
L
L L L L H L
H
H
H H H
H
H
H
L
L
L
L
H
H
L
H H
H
H H
H
L
H
L
L L
H H H L
H H
H
H H
H
H
L L L
H H
H
H
L
H
H H
H
L L H L L
H H H
H H
L
H
H H
H
L H
L
L
H H
H
H
H
H
L
H
H
L
H
H
L L
H
H H
H
H
H
H
L
H
H
H H
L L
H H H
H H H
H
H
L
X
X X
L L L H
H
H H
H
H
H H
X
X
X
H
L L
H
H H H
H
H H H
X
X
X L
H
L
H H
H
H H H H H
X X X
H
H L
H H
H H
H H
H H
X
X
X
H L
H H H
H
H
H
H
H H
X X
X
L H
H H H
H H
H
H
H
H
X X X
H H
H·
H H H
H
H
H H H
5-148