Up/Down Counter: Circuit, Working, and 74193 IC Details

In digital logic and computing, a circuit designed sequentially to tally up pulses is termed a counter. This counter IC consists of Flip-Flops (FFs) with a connected CLK signal, showcasing the primary use of FFs. These are engineered as individual integrated circuits (ICs) for widespread use in digital systems and within more expansive ICs. One such integral IC widely recognized for its Up/Down counting capabilities is the 74193 IC. Various counters exist, such as the Johnson counter, ripple or asynchronous, synchronous counter, decade, ring, and the Up/Down counter. This new technologies article delves into one specific type – the Up/Down counter, exploring its circuit, operation, applications, and how the 74193 IC fits into this landscape.

What is an Up/Down Counter?

The Up/Down counter often called the bidirectional counter, can count in varied directions depending on the state of its input control pin. They find use in various applications – some increment from zero, triggering a shift in output once a set value is reached. In contrast, others decrement from a specified number to zero, leading to a change in the output state. Certain counter models, such as the TTL 74LS190 and 74LS191, can operate in ascending and descending count modes, contingent on their up/down mode input pin status.

4-bit up/down counter

A 4-bit binary up/down counter sequence counts from 0000 to 1111 and then from 1111 back to 0000.

4-bit up/counter

A 4-bit down counter, with each clock pulse, tallies in sequence, producing outputs that count from 0 (0000) up to 15 (1111). 

4-bit down/counter

A 4-bit down counter is an electronic counter mechanism that facilitates a binary count-down, moving from 1111 to 0000. This configuration employs four D-type flip-flops that are activated by a positive edge. In this setup, each flip-flop channels its inverse output (/Q) back to its respective data input (D).

Synchronous 3-bit Up/Down Counter

The depicted circuit represents a straightforward 3-bit Up/Down synchronous counter constructed with JK flip-flops, set up to function as the toggle or T-type flip-flops. This allows it to count from zero (000) to seven (111) and revert to zero. Accordingly, the 3-Bit counter can increment in order (0,1,2,3,4,5,6,7) or decrement in the opposite sequence (7,6,5,4,3,2,1,0).

Up/Down Counter Circuit

Below is the circuit diagram of the 3-bit up/down counter, crafted using flip-flops. In the up-counter configuration, each flip-flop is triggered by the regular output (from the ‘Q’ output) of the preceding flip-flop, leading to the clock (CLK) of the next FF. Conversely, in the down-counter mode, every flip-flop is activated by the inverse output of the previous one, routing from the first FF’s output to the CLK of the subsequent FF.

How Does Up/Down Counter Work?

The up-down control input governs the functioning of the up/down counter. The counter operates in two distinct modes: count-up and count-down modes. The tables illustrating the count-up and count-down sequences are presented below.

Below is the table for the count-up mode.

States	QC	QB	QA
0	0	0	0
1	0	0	1
2	0	1	0
3	0	1	1
4	1	0	0
5	1	0	1
6	1	1	0
7	1	1	1

Below is the table for the count-down mode.

States	QC	QB	QA
7	1	1	1
6	1	1	0
5	1	0	1
4	1	0	0
3	0	1	1
2	0	1	0
1	0	0	1
0	0	0	0

For the up/down counting process, there are occasions where the subsequent flip-flop requires input from the Q output of the primary flip-flop to the CLK of the next FF for up-counting. At other times, it takes input from the Q^ output of the primary FF to the CLK of the next FF for down-counting. Typically, a single FF stores 1-bit, so a three-bit operation necessitates 3 FFs.

In the circuit described, there’s an inverter bridging the two control lines, namely count-up and count-down. This ensures that the count-up and count-down aren’t concurrently in the HIGH state.

When the count-up or count-down line is set to HIGH, the AND gates at the bottom become deactivated, resulting in their outputs reading zero. This doesn’t alter the OR gate outputs. At the same time, the top AND gates are activated. Consequently, ‘QA’ passes through the OR gate and reaches the B flip-flop’s CLK input. Similarly, ‘QB’ is directed to the CLK input of the C FF. So, when input signals are given, the counter increments, adhering to a standard binary count sequence from 000 to 111.

Conversely, if the count-up or count-down line remains LOW, the top AND gates are deactivated, and the bottom AND gates get activated. This action permits both the Q′A & Q′B outputs to channel through the CLK inputs of the FFs. Upon receiving input pulses, the counter initiates a descending count in this configuration.

How does the Up/Down Counter Count a Clock Pulse?

The up counter counts in ascending order, moving from the lowest to the highest value, while the down counter does the opposite, starting from the highest and descending to the lowest. In the Asynchronous 3-bit up/down counter, the counter's output is derived from the complemented outputs, termed as Q′, of the flip-flops (FFs) rather than their standard outputs. The initial count sequence is defined as QA QB QC = 111. With every negative clock edge, ‘QA’ alters its status. Similarly, when there’s a negative shift in the QA’ output, QB’ responds by toggling its state, and the same happens with QC’. As a result, with each clock pulse, the count decreases sequentially from 7 to 0.

For the up counter, each flip-flop is triggered by the standard output of the preceding FF (taking the ‘QA’ output from the main flip-flop to the clock input of the subsequent FF). Conversely, in the down counter, every flip-flop is engaged via the inverted output of the earlier FF (moving from the primary FF’s QA’ output to the CLK of the subsequent FF).

The first flip-flop is linked to a logic level of 0 for the up counter, triggering a toggle with every descending edge. The second flip-flop’s input is connected to the ‘QA’ of the first FF, causing a state change when QA is 1 during a falling clock edge. Similarly, the third flip-flop, connected to the second FF's ‘QB’, undergoes a state transition when QB registers 1 with a falling clock edge. This process crafts the counting states of the up counter. After every eighth descending edge, the counter resets to a 0 0 0 state.

The first flip-flop links to a logic 1 in the down counter scenario, prompting a toggle for each descending edge. The second flip-flop’s input attaches to the QA'  of the first FF, inducing a state change when QB’equals 1 at a falling clock edge. Similarly, the third FF, connected to the second FF's QB' , toggles its state when QB' is 1 during a falling clock edge. This mechanism facilitates the down counter's counting progression. After every eighth descending edge, the counter resets to the 0 0 0 configuration.

Up/Down Counter IC 74193

The 74193 IC, an example of an Up/Down counter, is a 4-bit synchronous Up/Down MODULO-16 binary counter. This chip comes with two CLK input pins, responsible for counting up and down to a specific value. As a result, its output synchronizes with the CLK inputs.

IC 74193 Up Down Counter

For advanced counter designs or to cascade this Up/Down counter IC, separate count Up and Count Down terminals are provided. Additionally, a master reset pin is integrated to reset the whole chip. An active low parallel load input pin also allows the counter to start from any given number.

74193 IC Pin Diagram

The IC 74193 is a 16-pin integrated circuit, and the functions of each pin are detailed below:

• Pin1 (CLR): An active-low reset input.

• Pin2 (CLK): A clock input signal.

• Pin3 (A (LSB), Pin4 (B), Pin5 (C) & Pin6 (D (MSB)): These pins are designated for data preset inputs.

• Pin7 (ENP): An active-high input labeled ENP.

• Pin8 (GND): Ground pin.

• Pin9 (Load): An active-low data load input.

• Pin10 (ENT): An active-high input labeled ENT.

• Pin11 (Qd (MSB)), Pin12 (Qc), Pin13 (Qb) & Pin14 (Qa (LSB)): These are the output pins of the flip-flops.

• Pin15 (RCO): Represents a ripple carry output transitioning from 0 to 1.

• Pin16 (Vcc): Power input pin.

Features

The features of IC 74193 are:

• It operates with a CLK frequency of 32MHz.

• The power usage is capped at 93mW.

• Functions as a 4-Bit Modulo-16 Up/Down counter.

• Comes with available preset inputs.

• Features synchronous programming.

• Has an internal ripple carry for efficient counting.

• Offers a carry output suitable for n-bit cascading.

• Boasts a propagation time of 14ns.

Up/Down Counter using IC 74193

The up/down counter using IC74193 is depicted as follows: The schematic demonstrates that Vcc links to pin-16 while the clear pins are anchored to the ground. Input signals are routed through pins 15, 10, 1, and 9, designated PA, PB, PC, and PD, respectively. Meanwhile, the output pins are labeled as 3, 2, 6, and 7, corresponding to QA, QB, QC, and QD. The inverter’s input pin connects to pin12 (carry), and its output attaches to IC’s load or pin11.

Up Down Counter using IC 74193

Within the circuit diagram, pin5 links to the clock up, while pin4 associates with the clock down. Activating pin4 to a high state causes the up/down counter to operate in down mode. Conversely, when pin5 goes high, the counter shifts to the up mode. Thus, this 74193 IC functions as a MOD Up/Down N counter.

What is the difference between Up and Down Counter?

up counter vs. down counter

up counter	down counter
The up counter tallies from '0' to its maximum limit.	The down counter starts from its peak value and descends to '0'.
It counts events in an ascending sequence.	It counts events in a descending sequence.

What are the Advantages and Disadvantages of Up/Down Counter?

The advantages of the up/down counter are as follows:

• Up/down counters can seamlessly integrate with high-speed configurations.

• They can increment or decrement synchronously based on the CLK’s transition from a low to a high state.

• Designing these counters with flip-flops is straightforward.

On the other hand, the disadvantages of the up/down counter are:

• Their use is limited as they tend to be imprecise at elevated clock speeds.

• An extra flip-flop is essential for re-synchronization.

• High CLK frequencies can introduce counting errors due to propagation delays.

• When dealing with many bits, these counters exhibit significant propagation delays.

Applications

The applications of up/down counter are as follows:

• It serves as an auto-reversing counter.

• The counter is applicable as a clock segmentation circuit.

• It’s employed in vehicle parking systems.

• These counters cater to applications requiring minimal noise and power consumption.

• They function as frequency partitioners.

• They play a pivotal role in crafting asynchronous ten-fold counters.

Conclusion

The intricacies of the Up/Down Counter, its functional framework, and the specificities of the 74193 IC have been elucidated in this article. With its unique ability to navigate ascending and descending sequences, this counter offers a wealth of applications from car parking systems to frequency division. The knowledge of its design, particularly with the 74193 IC, opens doors to leveraging its capabilities for various technological advancements. As technology evolves, understanding such foundational components becomes more crucial for innovators and enthusiasts alike.

Read More

• A Comprehensive Guide to Counter IC

• Synchronous and Asynchronous Counter: Key Differences Explained

• The Ultimate Guide to CD4017 Decade Counter IC: Datasheet & Its Application

• 74ls vs. 74hc series ICs

• What is a 4k7 Resistor？4.7k ohm Resistor Color Code

• 74LS93 4-Bit Binary Counter Pinout, Datasheet, Equivalent & Working

Previous: CD4017BE CMOS Counter: Circuit, Pinout and Datasheet

Next: The Ultimate Guide to Ring Counter: Working, Types & Applications