Figure 8.21. At the top are sample waves indicating what kind of input can be used to trigger the counter. The first one is a square wave. It consists of alternating 0 and 1 levels. Each period is the same length as all the others. The second wave is very irregular. Although it consists of alternating 0 and 1 levels no two periods are the same. The input feeds into the Ck input of flip-flop eh. The Q output goes to an output terminal labeled Q eh. The Q output also goes to the Ck input of flip-flop B. The Q output of B goes to the Q B output terminal and also to the Ck input of C. The Q output of C goes to the Q C output and also to the Ck input of D. The Q output of D goes to the Q D output terminal. The truth table is written below each flip-flop. This forces the binary numbers to be written backward. The columns are headed, left to right, Q eh, QB, QC, and QD. The first row is all zeros. Following rows are, 1 0 0 0, 0 1 0 0, 1 1 0 0, 0 0 1 0, 1 0 1 0, 0 1 1 0, 1 1 1 0, 0 0 0 1, 1 0 0 1, 0 1 0 1, 1 1 0 1, 0 0 1 1, 1 0 1 1, 0 1 1 1, 1 1 1 1. End verbal description.
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