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 Voltage | 4.75 – 5.25Vdc |
Maximum Clock Frequency | 40Mhz |
Power Dissipation | 2mW/gate @100kHz |
Minimum Output Current | 8mA |
Propagation Delay | 10nS |
Fan Out (TTL Loads) | 20 |
74LS191 Pinout Diagram

74LS191 Pin Description
Pin No | Pin Name | Description |
1 | B | Data Input Of Counter B |
2 | QB | Output Of Counter QB |
3 | QA | Output Of Counter QA |
4 | CTEN’ | Clock Enable |
5 | D/U’ | Down/Up(Active Low) |
6 | QC | Output Of Counter QC |
7 | QD | Output Of Counter QD |
8 | GND | Ground |
9 | D | Data Input Of Counter D |
10 | C | Data Input Of Counter V |
11 | LOAD’ | Load Pin(Active Low) |
12 | MAX/MIN | Maximum/Minimum |
13 | RCO’ | Ripple Carry Output(Active Low) |
14 | CLK | Clock Pin |
15 | A | Data Input Of Counter A |
16 | VCC | Positive Supply |
Applications
- 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.