HIT HD74HC85 Datasheet
HD74HC85
4-Bit Magnitude Comparator
Description
The HD74HC85 id designed for high speed comparison of two four bit words. This circuit has eight
comparison input, 4 for each word; three cascade inputs (A < B, A > B, A = B); and three decision outputs
(A < B, A > B, A = B). The result of a comparison is indicated by a high level on one of the decision
outputs. thus it may be determined whether one word is “greater than,” “less than,” or “equal to” the other
word. by connecting the outputs of the least significant stage to the cascade inputs of the enxt stage, words
of greater than four bits can be compared. In addition the least significant stage must have a high level
applied to the A = B input, and a low level to the A < B, and A > B inputs.
Features
• High Speed Operation: tpd (Data Word Input to Output) = 20 ns typ (CL = 50 pF)
• High Output Current: Fanout of 10 LSTTL Loads
• Wide Operating Voltage: VCC = 2 to 6 V
• Low Input Current: 1 µA max
• Low Quiescent Supply Current: ICC (static) = 4 µA max (Ta = 25°C)
HD74HC85
Function Table
Data Word Inputs Cascading Inputs Outputs
, B3A2, B
A
3
A3 > B3XXXXXXHLL
A
< B3XXXXXXLL H
3
A
= B3A2 > B2XXXXXHLL
3
A
= B3A2 < B2XXXXXLL H
3
A
= B3A2 = B2A1 > B1XXXXHLL
3
A
= B3A2 = B2A1 < B1XXXXLL H
3
A
= B3A2 = B2A1 = B1A0 > B0XXXHLL
3
A
= B3A2 = B2A1 = B1A0 < B0XXXLL H
3
A
= B3A2 = B2A1 = B1A0 = B0LLLHLH
3
A
= B3A2 = B2A1 = B1A0 = B0LLHLLH
3
A
= B3A2 = B2A1 = B1A0 = B0HL L HL L
3
A
= B3A2 = B2A1 = B1A0 = B0HL HL L L
3
A
= B3A2 = B2A1 = B1A0 = B0XHXLHL
3
A1, B
2
A0, B
1
A > Bin A = Bin A < Bin A > Bout A = Bout A < Bout
0
Pin Arrangement
3
B
Data
Input
A<B
A=B
A>B
A>B
A=B
A<B
GND
1
2
3
4
5
6
7
A<B
A=B
A>B
A>B
A=B
A<B
B3
B
In
out
0
A
B2
A2
A1
B1
A0
3
8
16
15
14
13
12
11
10
V
CC
A3
B2
A2
A1
B1
A0
9
B0
(Top view)
2
Logic Diagram
HD74HC85
B3
A3
A>Bout
B2
A2
B1
A1
A<Bout
B0
A0
A<Bin
A=Bin
A>Bin
A=Bout
3
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