Digital clocks

Thread Starter

Deborah Stephenson

Joined Apr 8, 2015
I my school books. The sections about counters were quite thorough. So the problem is more lazy students, I think. Since this is a popular assignment. I would say no complete schematics. A block digram may be OK. As it may give a push in the correct direction. But nothing more. We can not take all the fun from the students.
A student asked me how is a clock's rising or falling detected? I had never worried about this. I told him his question was beyond the purview of the class but would research. He hates rote memorization. I explained that in beginning ckts, they do not teach you how to make a resistor, capacitor, or inductor, only how to use them. But I too feel his question.


Joined Oct 2, 2009
What is a clock signal?

A clock signal is simply a transition from one logic level to another, for example, from logic LOW to logic HIGH, or from logic HIGH to logic LOW.

The introduction of a clock signal and time as a parameter is the essential difference between combinational circuits and sequential circuits.

In a combinational circuit, any change in an input will always produce the same output.

In a sequential circuit, a change in an input (i.e. the clock input) may result in a different output depending on the previous state of the circuit. Hence the function of the clock input is to move from one state to another. We present this pictorially in a state diagram.

See Mealy Machine: