Cascading Counters | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

Cascading Synchronous Counters

Connecting Synchronous counters in cascade, to obtain greater count ranges, is made simple in ICs such as the 74HC191 by using the ripple carry (Cascading Counters | Analog and Digital Electronics - Electrical Engineering (EE)) output of the IC counting the least significant 4 bits, to drive the clock input of the next most significant IC, as show in red in Fig. 5.6.17.

Although it may appear that either the TC or the  Cascading Counters | Analog and Digital Electronics - Electrical Engineering (EE) outputs could drive the next clock input, the TC output is not intended for this purpose, as timing issues can occur.

Cascading Counters | Analog and Digital Electronics - Electrical Engineering (EE)

 

Synchronous vs. Asynchronous Counters

Although synchronous counters have a great advantage over asynchronous or ripple counters in regard to reducing timing problems, there are situations where ripple counters have an advantage over synchronous counters.

When used at high speeds, only the first flip-flop in the ripple counter chain runs at the clock frequency. Each subsequent flip-flop runs at half the frequency of the previous one. In synchronous counters, with every stage operating at very high clock frequencies, stray capacitive coupling between the counter and other components and within the counter itself is more likely occur, so that in synchronous counters interference can be transferred between different stages of the counter, upsetting the count if adequate decoupling is not provided. This problem is reduced in ripple counters due to the lower frequencies in most of the stages.

Also, because the clock pulses applied to synchronous counters must charge, and discharge the input capacitance of every flip-flop simultaneously; synchronous counters having many flip-flops will cause large pulses of charge and discharge current in the clock driver circuits every time the clock changes logic state. This can also cause unwelcome spikes on the supply lines that could cause problems elsewhere in the digital circuitry. This is less of a problem with asynchronous counters, as the clock is only driving the first flip-flop in the counter chain.

Asynchronous counters are mostly used for frequency division applications and for generating time delays. In either of these applications the timing of individual outputs is not likely to cause a problem to external circuitry, and the fact that most of the stages in the counter run at much lower frequencies than the input clock, greatly reduces any problem of high frequency noise interference to surrounding components.

 

Counter ICs

synchronous (Ripple) Counters:

  • 74HC390 - Dual decade ripple counter from NXP.
  • 74HC393 - Dual 4-stage binary ripple counter from  ON Semiconductor.
  • 74HC4040 - 12-Stage binary ripple counter from Fairchild Semiconductor.
  • 74HC93 -- 4-Bit binary ripple counter from Texas instruments 
  • CD4060- 14-Stage binary counter plus oscillator from ST Microelectronics.
  • HEF4042B- 7-Stage binary ripple counter from NXP.
  •  

Synchronous Counters:

  • 74HC160 - Pre-settable synchronous BCD counter with asynchronous reset from NXP.
  • 74HC161 - 4-Bit synchronous BCD counter with asynchronous reset and synchronous load from Texas instruments 
  • 74HC163 - 4-Bit synchronous binary counter with asynchronous reset and synchronous load from Texas instruments .
  • 74HC191 - 4-bit synchronous binary up/down counter with asynchronous reset and load from NXP.
  • 74HC192  - 4-Bit synchronous BCD counter with asynchronous reset and load from Texas instruments 
  • 74HC193  - 4-Bit synchronous binary counter with asynchronous reset and load from Texas instruments 
  •  CD4017/4022B- 4-Stage synchronous counters with Decade (1 of 10) or Octal (1 of 8) outputs from Texas instruments.
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FAQs on Cascading Counters - Analog and Digital Electronics - Electrical Engineering (EE)

1. What are cascading counters?
Cascading counters refer to a method of connecting multiple counters together in a series, where the output of each counter is connected to the input of the next counter. This allows for counting of larger numbers by combining the count values of each individual counter.
2. How do cascading counters work?
In cascading counters, the output of one counter acts as the input for the next counter. When the first counter reaches its maximum count and overflows, it sends a signal to increment the next counter. This process continues until the final counter overflows, providing a complete count of the desired number.
3. What are the advantages of using cascading counters?
Cascading counters offer several advantages. Firstly, they allow for counting larger numbers that cannot be accommodated by a single counter. Additionally, cascading counters provide a modular and flexible approach, as individual counters can be easily added or removed to adjust the counting range as needed.
4. Can cascading counters be used for complex calculations?
No, cascading counters are primarily used for simple counting tasks. They are not meant for performing complex calculations or mathematical operations. Instead, their main purpose is to extend the counting range beyond what a single counter can handle.
5. Are cascading counters commonly used in digital electronics?
Yes, cascading counters are widely used in digital electronics. They are commonly employed in applications such as frequency dividers, event counters, and timing circuits. By connecting multiple counters in a cascading arrangement, digital systems can effectively count and track events or signals.
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