HD74HC182
Look-Ahead Carry Generator
Description
The HD74HC182 is a high-speed Carry Lockahead Generator. It is used with the HD74HC181 4-Bit
Arithmetic Logic Unit to provide high-speed lockahead over World lengths of more than four bits. The
device accepts up to four pairs of active-low Carry Propagate (P
0
, P
1
, P
2
, P
3
) and Carry Generate (G
0
, G
1
,
G
2
, G
3
) signals and an active-high carries (C
n+x
, C
n+y,
C
n+z
) across four groups of binary adders. The
HD74HC182 also has active-low Carry Propagate (P) and Carry Generate (G) outputs which may be used
for further levels of lockahead.
The logic equations provided at the outputs are:
C
n+x
= Y
0
(X
0
+ C
n
)
C
n+y
= Y
1
{X
1
+ Y
0
(X
0
+ C
n
)}
C
n+z
= Y
2
[X
2
+ Y
1
{X
1
+ Y
0
(X
0
+ C
n
)}]
Y = Y
3
(X
3
+ Y
2
) (X
3
+ X
2
+ Y
1
) (X
3
+ X
2
+ X
1
+ Y
0
)
X = X
3
+ X
2
+ X
1
+ X
0
or
C
n+x
= G
0
+ P
0
C
n
C
n+y
= G
1
+ P
1
G
0
+ P
1
P
0
C
n
C
n+z
= G
2
+ P
2
G
1
+ P
2
P
1
G
0
+ P
2
P
1
P
0
C
n
G = G
3
+ P
3
G
2
+ P
3
P
2
G
1
+ P
3
P
2
P
1
G
0
P
= P
3
P
2
P
1
P
0
Also, the HD74HC182 can be used with binary ALUs in an active-low or active-high input operand mode.
The connections to and from the ALU to the carry lookahead generator are identical in both cases.
HD74HC182
Features
•
High Speed Operation: t
pd
(Pn to P) = 11 ns typ (C
L
= 50 pF)
•
High Output Current: Fanout of 10 LSTTL Loads
•
Wide Operating Voltage: V
CC
= 2 to 6 V
•
Low Input Current: 1 µA max
•
Low Quiescent Supply Current: I
CC
(static) = 4 µA max (Ta = 25°C)
Pin Designations
Item
G
0
, G
1
, G
2
, G
3
P
0
, P
1
, P
2
, P
3
C
n
C
n+x
, C
n+y
, C
n+z
G
P
V
CC
GND
Pin No.
3, 1, 14, 5
4, 2, 15, 6
13
12, 11, 9
10
7
16
8
Functions
Active-low carry generate inputs
Active-low carry propagate inputs
Carry input
Carry outputs
Active-low carry propagate output
Active-low carry propagate output
Supply voltage
Ground
2
Microcontroller MCU
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