74LS191 Up/Down Binary Counter


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. The 74LS191 is synchronous, reversible up/down counters having a complexity of 58 equivalent gates.

74LS191 Features

  • Synchronous Up/Down Mudulo-16 Binary Counter, Count is Updated with Low-to-High Clock Transition
  • Synchronous Counting
  • High Speed up to 25MHz
  • Individual Preset Inputs
  • Standard TTL Switching Voltages

74LS191 Specifications

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

74LS191 Pinout Diagram

74LS191 Pin Description

Pin NoPin NameDescription
1BData Input Of Counter B
2QBOutput Of Counter QB
3QAOutput Of Counter QA
4CTEN’Clock Enable
5D/U’Down/Up(Active Low)
6QCOutput Of Counter QC
7QDOutput Of Counter QD
9DData Input Of Counter D
10CData Input Of Counter V
11LOAD’Load Pin(Active Low)
13RCO’Ripple Carry Output(Active Low)
14CLKClock Pin
15AData Input Of Counter A
16VCCPositive Supply


  • Frequency counters
  • Digital clocks
  • Analog to digital converters
  • With some changes in their design, counters can be used as frequency divider circuits
  • In time measurement

74LS191 Alternative Equivalent

Download the 74LS191 Up/Down Binary Counter Datasheet from the link given below.