74191 (4-bit Up/Down Binary Counter )

Description

The 74191 is a 4-bit Up/Down Binary Counter with Synchronous Parallel Load. It is part of the 7400 series and is used for counting applications, where it counts in either an up or down direction based on control inputs. This IC is widely used in digital systems that require binary counting, such as frequency counters, digital clocks, timers, and other counting systems.

74191 IC Description:

The 74191 is a synchronous 4-bit up/down binary counter that can count in either direction. It is designed to be used in systems where counting needs to be done in a precise and controlled manner. The counter can be loaded with a 4-bit value via parallel inputs and will count either up or down depending on the control inputs. The 74191 also includes a synchronous reset function and operates in synchronous mode, meaning all bits change in sync with the clock pulse.

Key Features:

• 4-bit Up/Down Counter: The 74191 has a 4-bit binary counter, which means it can count from 0 to 15 in binary (0000 to 1111).
• Synchronous Parallel Load: It has the ability to load a 4-bit parallel value into the counter when needed, which can be done asynchronously with the counting process.
• Up/Down Control: The counter can count either up (incrementing) or down (decrementing) based on the state of the Up/Down (U/D) control pin.
• Clocked Operation: The counter changes state based on the clock (CLK) input. All bits change synchronously on the rising edge of the clock.
• Asynchronous Reset (CLEAR): The counter has an active-low Clear pin that resets the counter to 0000 when triggered.
• Carry Output (CO): The Carry Output is used to indicate when the counter has reached its maximum or minimum value, and it can be connected to other counters to cascade them for counting larger numbers.

Pin Configuration (16-pin package):

Here’s the pinout for the 74191 4-bit Up/Down Counter:

1. Pin 1 (Q0): Output bit 0 (Least Significant Bit).
2. Pin 2 (Q1): Output bit 1.
3. Pin 3 (Q2): Output bit 2.
4. Pin 4 (Q3): Output bit 3 (Most Significant Bit).
5. Pin 5 (Carry Output): CO – Carry output for cascading counters.
6. Pin 6 (Clear): Active-low Clear input for resetting the counter.
7. Pin 7 (Up/Down): Control input for counting direction. High = Up, Low = Down.
8. Pin 8 (Clock): CLK – Clock input for synchronizing counting.
9. Pin 9 (Parallel Data Input D0 to D3): Parallel data inputs for loading a 4-bit value into the counter.
10. Pin 10 (Load): Load pin, used to enable parallel loading of the counter with the data on D0 to D3.
11. Pin 11 (Vcc): Supply voltage (typically 5V).
12. Pin 12 (D0): Parallel data input bit 0.
13. Pin 13 (D1): Parallel data input bit 1.
14. Pin 14 (D2): Parallel data input bit 2.
15. Pin 15 (D3): Parallel data input bit 3.
16. Pin 16 (Ground): Ground.

How It Works:

1. Counting Operation:
   • When the Up/Down (U/D) pin is high, the counter will increment (count up) on each rising clock edge.
   • When the Up/Down (U/D) pin is low, the counter will decrement (count down) on each rising clock edge.
   • The counter will change its value synchronously with the clock, meaning all bits change simultaneously on the rising edge of the clock.
2. Parallel Load:
   • The 74191 has a parallel load feature, where you can load a 4-bit binary number into the counter using the D0 to D3 pins.
   • The Load (LD) pin must be held low to enable this function. When the load pin is low, the value on the D0 to D3 inputs is loaded into the counter immediately, overriding any counting action.
3. Clear:
   • The Clear (CLR) pin is active-low, meaning when it is low, it will reset the counter to 0000, regardless of the clock input.
4. Carry Output (CO):
   • The Carry Output (CO) is a pulse that is generated when the counter reaches its maximum or minimum count. This pulse can be used to cascade multiple counters together to create larger binary counts (for example, a 16-bit or 32-bit counter).
5. Clocking:
   • The counter changes its state on the rising edge of the clock signal. It operates synchronously, meaning all bits (Q0 to Q3) change at the same time.

Truth Table:

Applications:

1. Digital Counters: The 74191 is commonly used in digital counting applications, such as event counters, frequency counters, or any system that requires binary counting from 0 to 15.
2. Frequency Dividers: In digital systems, the 74191 can be used as a frequency divider, where it counts clock pulses and generates a divided output when it reaches a certain value.
3. Timers and Clocks: The counter can be used to build timing circuits or digital clocks where precise counting of seconds, minutes, or other units is required.
4. Up/Down Counting Systems: The 74191 can be used in applications where the counting direction needs to be controlled, such as in systems where values need to be incremented or decremented based on external conditions or inputs.
5. Event-Counting Applications: It is useful for event counting in systems that need to track occurrences of certain events and either increment or decrement the count.
6. Multi-Stage Counters: When multiple 74191 ICs are cascaded using the Carry Output (CO) pin, they can create larger counters, such as 8-bit, 16-bit, or even higher counters.
7. Digital Arithmetic Circuits: It can be used in systems that perform arithmetic operations (such as addition or subtraction) using binary counters.

Electrical Characteristics:

• Supply Voltage (Vcc): Typically 5V (can operate in the range of 4.5V to 5.5V).
• Clock Frequency: The speed of operation depends on the clock frequency. The 74191 typically operates at frequencies up to a few MHz, depending on the application.
• Low Power Consumption: Being a CMOS-based IC, the 74191 has low power consumption.

Example Circuit:

In a digital clock system, the 74191 could be used to count the seconds, minutes, or hours. A clock signal would drive the 74191, incrementing the count in the up direction. When the counter reaches the required value (for example, 60 for seconds), the Carry Output (CO) would trigger the next stage of counting (minutes), or reset the counter to 0.