In the previous section, we studied combinational logic. We have approached our study of Boolean functions by examining the variables, the values for those variables, and the function outputs that depend solely on the values of the inputs to the functions. If we change an input value, this has a direct and immediate effect on the value of the output. The major weakness of combinational circuits is that there is no concept of storage—they are memoryless. This presents us with a dilemma. We know that computers must have a way to remember values. Consider a much simpler digital circuit needed for a soda machine. When you put money into a soda machine, the machine remembers how much you have put in at any given instant. ...

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