HIT HD74HC688 Datasheet

HD74HC688

8-bit Magnitude Comparator

Description

The HD74HC688 compares bit for bit two 8-bit words and indicates whether or not they are equal. The
P=Q output indicates equality when it is low.

A single active low enable is provided to facilitate cascading of several packages and enable comparison of
words greater than 8-bits.

This device is useful in memory block decoding applications, where memory block enable signals must be
generated from computer address information.

Features

• High Speed Operation: tpd (P or Q to Output) = 17 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)

Function Table

Input
Data P, Q Enable G P=Q

P=Q L L
P>Q L H
P<Q L H
XH H

HD74HC688

Pin Arrangement

G

1

P

2

0

20
19

V

CC

P=Q

Q

P

Q

P

Q

P

Q

GND

3

0

4

1

5

1

6

2

7

2

8

3

9

3

10

18
17
16
15
14
13
12
11

Q

7

P

7

Q

6

P

6

Q

5

P

5

Q

4

Q

4

(Top view)

2

Block Diagram

HD74HC688

P

0

Q

0

P

1

Q

1

P

2

Q

2

P

3

Q

3

P

4

P=Q

Q

4

P

5

Q

5

P

6

Q

6

P

7

Q

7

G

3