74LS688 8-bit Magnitude Comparator


The 74LS series of integrated circuits (ICs) was one of the most popular logic families of transistor-transistor logic (TTL) logic chips. 74LS series is a bipolar, low-power Schottky IC.74LS688 is an 8-bit magnitude comparator. 74LS688 is designed to perform comparisons between two eight-bit binary or BCD words. All device types provide P = Q outputs and the LS682 and LS684 have P>Q outputs also.

74LS688 Features

  • Designed to Perform Comparisons Between Two 8-bit Binary or BCD Words
  • Totem Pole Output
  • Provides Equal Comparison Result
  • Operating Temperature up to 70°C
  • Standard TTL Switching Voltages

74LS688 Specifications

Supply Voltage4.75 – 5.25Vdc
Maximum Clock Frequency40Mhz
Power Dissipation2mW/gate @100kHz
Minimum Output Current8mA
Propagation Delay10nS
Fan Out (TTL Loads)20

74LS688 Pinout Diagram

74LS688 Pin Description

Pin NoPin NameDescription
1G’Enable Input(Active Low)
2P0Bit 0 of Comparator 1
3Q0Bit 0 of Comparator 2
4P1Bit 1 of Comparator 1
5Q1Bit 1 of Comparator 2
6P2Bit 2 of Comparator 1
7Q2Bit 2 of Comparator 2
8P3Bit 3 of Comparator 1
9Q3Bit 3 of Comparator 2
11P4Bit 4 of Comparator 1
12Q4Bit 4 of Comparator 2
13P5Bit 5 of Comparator 1
14Q5Bit 5 of Comparator 2
15P6Bit 6 of Comparator 1
16Q6Bit 6 of Comparator 2
17P7Bit 7 of Comparator 1
18Q7Bit 7 of Comparator 2
19P’=Q’Comparator Equal Output Pin
20VCCPositive Supply

74LS688 Circuit

Below is a circuit of 1-bit magnitude comparator using logic gates (NOT, AND, and NOR).


  • Null detectors
  • Zero-crossing detectors
  • Relaxation oscillator
  • Level shifter
  • Analog-to-digital converters
  • Window detectors

74LS688 Alternative Equivalent


Download 74LS688 8-bit Magnitude Comparator Datasheet from the link given below.