74F148 8-Line to 3-Line Priority Encoder
April 1988
Revised July 1999
74F148
8-Line to 3-Line Priority Encoder
General Description
The F148 provides three bits of binary coded output repre-
senting the position of the highest order active input, along
with an output indicating the presence of any active input. It
is easily expanded via input and output enables to provide
priority encoding over many bits.
Features
s
Encodes eight data lines in priority
s
Provides 3-bit binary priority code
s
Input enable capability
s
Signals when data is present on any input
s
Cascadable for priority encoding of n bits
Ordering Code:
Order Number
74F148SC
74F148SJ
74F148PC
Package Number
M16A
M16D
N16E
Package Description
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Logic Symbols
Connection Diagram
IEEE/IEC
Truth Table
Inputs
EI
H
L
L
L
L
L
L
L
L
L
I
0
X
H
X
X
X
X
X
X
X
L
I
1
X
H
X
X
X
X
X
X
L
H
I
2
X
H
X
X
X
X
X
L
H
H
I
3
X
H
X
X
X
X
L
H
H
H
I
4
X
H
X
X
X
L
H
H
H
H
I
5
X
H
X
X
L
H
H
H
H
H
I
6
X
H
X
L
H
H
H
H
H
H
Outputs
I
7
GS A
0
A
1
A
2
EO
X
H
L
H
H
H
H
H
H
H
H
H
L
L
L
L
L
L
L
L
H
H
L
H
L
H
L
H
L
H
H
H
L
L
H
H
L
L
H
H
H
H
L
L
L
L
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
=
HIGH Voltage Level
L
=
LOW Voltage Level
X
=
Immaterial
© 1999 Fairchild Semiconductor Corporation
DS009480
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74F148
Unit Loading/Fan Out
U.L.
Pin Names
I
0
I
1
–I
7
EI
EO
GS
A
0
–A
2
Description
HIGH/LOW
Priority Input (Active LOW)
Priority Inputs (Active LOW)
Enable Input (Active LOW)
Enable Output (Active LOW)
Group Signal Output (Active LOW)
Address Outputs (Active LOW)
1.0/1.0
1.0/2.0
1.0/1.0
50/33.3
50/33.3
50/33.3
Input I
IH
/I
IL
Output I
OH
/I
OL
20
µA/−0.6
mA
20
µA/−1.2
mA
20
µA/−0.6
mA
−1
mA/20 mA
−1
mA/20 mA
−1
mA/20 mA
Functional Description
The F148 8-input priority encoder accepts data from eight
active LOW inputs (I
0
–I
7
) and provides a binary represen-
tation on the three active LOW outputs. A priority is
assigned to each input so that when two or more inputs are
simultaneously active, the input with the highest priority is
represented on the output, with input line 7 having the high-
est priority. A HIGH on the Enable Input (EI) will force all
outputs to the inactive (HIGH) state and allow new data to
settle without producing erroneous information at the out-
puts.A Group Signal output (GS) and Enable Output (EO)
are provided along with the three priority data outputs (A
2
,
A
1
, A
0
). GS is active LOW when any input is LOW: this
indicates when any input is active. EO is active LOW when
all inputs are HIGH. Using the Enable Output along with
the Enable Input allows cascading for priority encoding on
any number of input signals. Both EO and GS are in the
inactive HIGH state when the Enable Input is HIGH.
Logic Diagram
Application
16-Input Priority Encoder
Please note that this diagram is provided only for the understanding of logic
operations and should not be used to estimate propagation delays.
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2
74F148
Absolute Maximum Ratings
(Note 1)
Storage Temperature
Ambient Temperature under Bias
Junction Temperature under Bias
V
CC
Pin Potential to Ground Pin
Input Voltage (Note 2)
Input Current (Note 2)
Voltage Applied to Output
in HIGH State (with V
CC
=
0V)
Standard Output
3-STATE Output
Current Applied to Output
in LOW State (Max)
twice the rated I
OL
(mA)
−0.5V
to V
CC
−0.5V
to
+5.5V
−65°C
to
+150°C
−55°C
to
+125°C
−55°C
to
+150°C
−0.5V
to
+7.0V
−0.5V
to
+7.0V
−30
mA to
+5.0
mA
Recommended Operating
Conditions
Free Air Ambient Temperature
Supply Voltage
0°C to
+70°C
+4.5V
to
+5.5V
Note 1:
Absolute maximum ratings are values beyond which the device
may be damaged or have its useful life impaired. Functional operation
under these conditions is not implied.
Note 2:
Either voltage limit or current limit is sufficient to protect inputs.
DC Electrical Characteristics
Symbol
V
IH
V
IL
V
CD
V
OH
V
OL
I
IH
I
BVI
I
CEX
V
ID
I
OD
I
IL
Parameter
Input HIGH Voltage
Input LOW Voltage
Input Clamp Diode Voltage
Output HIGH
Voltage
Output LOW
Voltage
Input HIGH
Current
Input HIGH Current
Breakdown Test
Output High
Leakage Current
Input Leakage
Test
Output Leakage
Circuit Current
Input LOW
Current
I
OS
I
CCH
I
CCL
Output Short-Circuit Current
Power Supply Current
Power Supply Current
−60
4.75
3.75
−0.6
−1.2
−150
35
35
10% V
CC
5% V
CC
10% V
CC
2.5
2.7
0.5
5.0
7.0
50
Min
2.0
0.8
−1.2
Typ
Max
Units
V
V
V
V
V
µA
µA
µA
V
µA
mA
mA
mA
mA
mA
Max
Max
Max
Min
Min
Min
Max
Max
Max
0.0
0.0
Max
V
CC
Conditions
Recognized as a HIGH Signal
Recognized as a LOW Signal
I
IN
= −18
mA
I
OH
= −1
mA
I
OH
= −1
mA
I
OL
=
20 mA
V
IN
=
2.7V
V
IN
=
7.0V
V
OUT
=
V
CC
I
ID
=
1.9
µA
All Other Pins Grounded
V
IOD
=
150 mV
All Other Pins Grounded
V
IN
=
0.5V (I
0
, EI)
V
IN
=
0.5V (I
1
–I
7
)
V
OUT
=
0V
V
O
=
HIGH
V
O
=
LOW
3
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74F148
AC Electrical Characteristics
T
A
= +25°C
Symbol
Parameter
Min
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
Propagation Delay
I
n
to A
n
Propagation Delay
I
n
to EO
Propagation Delay
I
n
to GS
Propagation Delay
EI to A
n
Propagation Delay
EI to GS
Propagation Delay
EI to EO
3.0
3.0
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
3.0
V
CC
= +5.0V
C
L
=
50 pF
Typ
7.0
8.0
5.0
5.5
7.0
6.0
6.5
6.0
5.0
6.0
5.5
8.0
Max
9.0
10.5
6.5
7.5
9.0
8.0
8.5
8.0
7.0
7.5
7.0
10.5
T
A
=
0°C to
+70°C
V
CC
= +5.0V
C
L
=
50 pF
Min
3.0
3.0
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
3.0
Max
10.0
12.0
7.5
8.5
10.0
9.0
9.5
9.0
8.0
8.5
8.0
12.0
ns
Units
ns
ns
ns
ns
ns
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4
74F148
Physical Dimensions
inches (millimeters) unless otherwise noted
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
Package Number M16A
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
Package Number M16D
5
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