HIT HD74HCT688 Datasheet

HD74HCT688

8-bit Magnitude Comparator

Description

The HD74HCT688 compares bit for bit two 8-bit words and indicate 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

• LSTTL Output Logic Level Compatibility as well as CMOS Output Compatibility

• High Speed Operation: tpd (Data to P=Q) = 18 ns typ (CL = 50 pF)

• High Output Current: Fanout of 10 LSTTL Loads

• Wide Operating Voltage: VCC = 4.5 to 5.5 V

• Low Input Current: 1 µA max

• Low Quiescent Supply Current: ICC (static) = 4 µA max (Ta = 25°C)

Function Table

Inputs
Data P, Q Enable G P=Q

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

HD74HCT688

Pin Arrangement

G

1

P

2

0

20
19

V

CC

P=Q

Q0

P1

Q1

P2

Q2

P3

Q3

GND

10

3
4
5
6
7
8
9

(Top view)

18
17
16
15
14
13
12
11

Q
P7
Q6
P6
Q5
P5
Q4
P4

7

2

Block Diagram

Q

HD74HCT688

P0

Q0

P1

Q1

P2

Q2

P3

Q3

P4

P=

Q4

P5

Q5

P6

Q6

P7

Q7

G

3