Model
5340A
Theory of Operation
-
4
-
57.
Eight
-
input Priority Encoder
1820
-
0657
1
4
-
58.
Figure
4
-
26
shows the logic diagram, and outline drawing, for the
1820
-
0657.
This IC
accepts eight active low inputs and produces a binary weighted output corresponding to the
highest order input. Priorities are assigned to each active low input
so
that when two or more
inputs are simultaneously active, the input with the
highest priority appears
at
the output.
-
Input
7
has the highest priority.
An
active low enable input
(El)
and active low enable output (EO) are
provided to expand priority encoding to more inputs.
"&is
mode
of
operation
is
acheived by
connecting the
-
more significant encoder's enable output
(EO)
to the next less significant encoder
enable
-
input
(El).
In addition,
a
group signal
is
provided which
is
active if any input
is
active
and
El
is
low. As an example of encoder operation, assume that input
2
and
6
are
low
and
El
is
low. In this case, the encoder gives priority to the
6
input and gives
a
binary output of
AO=H,
Al=L,
and
A2=L.
Figure
4
-
26.
Eight
-
Input Priority Encoder
1820
-
0657
PIN
NAMES
0
El
EO
G5
1107
b.
A1
1
A2
Priority (Active
LOW1
Input
Priority
(Actlve
LOW)
Inputs
Enable (Active
LOW)
Input
Enable (Active
LOW)
Output
Group Select (Active
LOW1
Output
Address (Active
LOW)
Outpuls
I0
1112
13
12
3
4
5
15976
14
Vcc
=Pin
16
GND
=Pin
8
'IN
NUMBERS
NOTES
a
1
Unit
Load
IU
L
I
40
PA HIGH/l
6
mA
LOW
10
U
L
IS
the
out~u1
LOW drive
factor
and
20
U
L
IS
the
OU~PU~
HIGH
drive fact08
,
I
I,
4
-
18
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