Lockout Condition in Counter

A digital counter is a sequential logic circuit which counts the number of clock pulses or events that occur over time. Now, let us discuss the lockout condition in counter.

What is Lockout Condition in Counter?

In digital counters, the condition wherein the counter enters to an unused state and rather than coming out of this unused state to a valid state or initial state, it switches to another invalid or unused state and gets stuck up in the cycle of unused states only, is known as the lockout condition in the counter.

Therefore, in the case of lockout condition, the counter stops counting further. In counters, the lockout condition occurs due to some internal or external events.

Depending on the type of counter and its application, the lockout conditions can be classified into the following major types −

  • Internal Lockout Condition − When the counter detects an internal event or fault and stops counting, then this is called internal lockout condition.

  • External Lockout Condition − When the lockout of the counter occurs due to some external events so that the counter stops counting, it is called external lockout condition.

  • Minimum Count Lockout − When the counter is designed for down counting and it counts down to a minimum value and then stops counting, this is called minimum count lockout condition.

  • Maximum Count Lockout − When the counter is designed for up counting and it counts up to a maximum value and then stops counting, this is called maximum count lockout condition.

Effects of Lockout Condition in Counter

As we mentioned above that the lockout condition in a counter prevents it from counting. There could be many reasons of lockout condition such as faulty clock pulse, improper reset signal, etc. Basically, the lockout condition can cause the counter to stop counting or freeze at a particular state or go into an unused state.

The lockout condition in a counter can cause several undesirable effects. Some common of them are listed here −

  • Due to lockout condition, the counter either stops counting or freezes at a particular state or goes into an unused state. Hence, the lockout condition in a counter can produce incorrect count results.

  • A counter which is designed to detect and avoid the lockout condition requires additional logic circuitry. This increases the complexity as well as cost of the counter.

  • Lockout condition in counter results in a delayed response, hence it reduces the performance of the system.

  • Lockout condition also reduces the overall reliability of the digital system.

Therefore, it is important to design the counter that can detect and correct the undesired lockout conditions.

In digital counters, the lockout condition can be desirable or undesirable. When the lockout condition is desirable in a counter, then it prevents the counter to produce inaccurate results. But, when it is undesirable, then it should be avoided. The undesired lockout condition in counters may be avoided as described below.

How to Avoid Lockout Condition in Counter?

The undesired lockout condition in a counter can be avoided by designing the counter in such a way that whenever the counter enter to an unused state, then the next state must be a used state. So that the counter go from the unused state to a known used state.


In conclusion, the lockout condition in a counter is a condition in which the counter goes into an unused state and is not able to arrive at a used state itself. Sometimes, the lockout condition is useful in counters because it prevent the undesired results from the counter.

Updated on: 24-Apr-2023


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