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Digital Fundamentals
CHAPTER
ELEVENTH EDITION
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Counters
9
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FIGURE 9-1 Two types of sequential logic.
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FIGURE 9-2 A fixed-modulus binary counter as an example of a Moore state machine. The dashed line in the state diagram means the states between binary 1 and 25 are not shown for simplicity.
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FIGURE 9-3 A variable-modulus binary counter as an example of a Mealy state machine. The red arrows in the state diagram represent the recycle paths that depend on the input number. The black dashed lines mean the interim states are not shown for simplicity.
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FIGURE 9-4 A 2-bit asynchronous binary counter.
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FIGURE 9-5 Timing diagram for the counter of Figure 9-4. As in previous chapters, output waveforms are shown in green.
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TABLE 9–1 Binary state sequence for the counter in Figure 9–4.
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TABLE 9–2 State sequence for a 3-bit binary counter.
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FIGURE 9-6 Three-bit asynchronous binary counter and its timing diagram for one cycle.
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FIGURE 9-7 Propagation delays in a 3-bit asynchronous (ripple-clocked) binary counter.
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FIGURE 9-8 Four-bit asynchronous binary counter and its timing diagram.
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FIGURE 9-9 An asynchronously clocked decade counter with asynchronous recycling.
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FIGURE 9-10 Asynchronously clocked modulus-12 counter with asynchronous recycling.
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FIGURE 9-11 Two configurations of the 74HC93 asynchronous counter. (The qualifying label, CTR DIV n, indicates a counter with n states.)
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FIGURE 9-12 2-bit synchronous binary counters.
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FIGURE 9-13 Timing details for the 2-bit synchronous counter operation (the propagation delays of both flip-flops are assumed to be equal).
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FIGURE 9-14 Timing diagram for the counters of Figure 9-12.
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FIGURE 9-15 A 3-bit synchronous binary counter.
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FIGURE 9-16 Timing diagram for the counter of Figure 9-15.
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TABLE 9–3 State sequence for a 3-bit binary counter.
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TABLE 9–4 Summary of the analysis of the counter in Figure 9–15.
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FIGURE 9-17 A 4-bit synchronous binary counter and timing diagram. Times where the AND gate outputs are HIGH are indicated by the shaded areas.
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FIGURE 9-18 A synchronous BCD decade counter.
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FIGURE 9-19 Timing diagram for the BCD decade counter (Q0 is the LSB).
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TABLE 9–5 States of a BCD decade counter.
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FIGURE 9-20 The 74HC163 4-bit synchronous binary counter. (The qualifying label CTR DIV 16 indicates a counter with sixteen states.)
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FIGURE 9-21 Timing example for a 74HC163.
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TABLE 9–6 Up/Down sequence for a 3-bit binary counter.
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FIGURE 9-22 A basic 3-bit up/down synchronous counter.
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FIGURE 9-23
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TABLE 9–7
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FIGURE 9-24 The 74HC190 up/down synchronous decade counter.
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FIGURE 9-25 Timing example for a 74HC190.
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FIGURE 9-26 State diagram for a 3-bit Gray code counter.
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TABLE 9–8 Next-state table for 3-bit Gray code counter.
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TABLE 9–9 Transition table for a J-K flip-flop.
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FIGURE 9-27 Examples of the mapping procedure for the counter sequence represented in Table 9–8 and Table 9–9.
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FIGURE 9-28 Karnaugh maps for present-state J and K inputs.
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FIGURE 9-29 Three-bit Gray code counter.
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FIGURE 9-30
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TABLE 9–10 Next-state table.
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TABLE 9–11 Transition table for a D flip-flop.
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FIGURE 9-31
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FIGURE 9-32
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FIGURE 9-33 State diagram for a 3-bit up/down Gray code counter.
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TABLE 9–12 Next-state table for 3-bit up/down Gray code counter.
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TABLE 9–13 Transition table for a J-K flip-flop.
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FIGURE 9-34 J and K maps for Table 9–12. The UP/DOWN control input, Y, is treated as a fourth variable.
_____
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FIGURE 9-35 Two cascaded asynchronous counters (all J and K inputs are HIGH).
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FIGURE 9-36 Timing diagram for the cascaded counter configuration of Figure 9-35.
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FIGURE 9-37 A modulus-100 counter using two cascaded decade counters.
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FIGURE 9-38 Three cascaded decade counters forming a divide-by-1000 frequency divider with intermediate divide-by-10 and divide-by-100 outputs.
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FIGURE 9-39
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FIGURE 9-40 A divide-by-100 counter using two 74HC190 up/down decade counters connected for the up sequence.
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FIGURE 9-41 A divide-by-40,000 counter using 74HC161 4-bit binary counters. Note that each of the parallel data inputs is shown in binary order (the right-most bit D0 is the LSB in each counter).
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FIGURE 9-42 Decoding of state 6 (110).
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FIGURE 9-43 A 3-bit counter with active-HIGH decoding of count 2 and count 7.
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FIGURE 9-44 A basic decade (BCD) counter and decoder.
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FIGURE 9-45 Outputs with glitches from the decoder in Figure 9-44. Glitch widths are exaggerated for illustration and are usually only a few nanoseconds wide.
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FIGURE 9-46 The basic decade counter and decoder with strobing to eliminate glitches.
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FIGURE 9-47 Strobed decoder outputs for the circuit of Figure 9-46.
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FIGURE 9-48 Simplified logic diagram for a 12-hour digital clock. Logic details using specific devices are shown in Figures 9-49 and 9-50.
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FIGURE 9-49 Logic diagram of typical divide-by-60 counter using synchronous decade counters. Note that the outputs are in binary order (the right-most bit is the LSB).
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FIGURE 9-50 GS Logic diagram for hours counter and decoders. Note that on the counter inputs and outputs, the right-most bit is the LSB.
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FIGURE 9-51 Functional block diagram for parking garage control.
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FIGURE 9-52 Logic diagram for modulus-100 up/down counter for automobile parking control.
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FIGURE 9-53 Parallel-to-serial data conversion logic.
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FIGURE 9-54 Example of parallel-to-serial conversion timing for the circuit in Figure 9-53.
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FIGURE 9-55 The 74HC163 4-bit synchronous counter.
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FIGURE 9-56 Example of a failure that affects following counters in a cascaded arrangement.
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FIGURE 9-57 Example of a failure in a cascaded counter with a truncated sequence.
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FIGURE 9-58
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FIGURE 9-59
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FIGURE 9-60 One cycle of the elevator operation.
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FIGURE 9-61 Elevator controller state diagram.
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FIGURE 9-62 Elevator controller block diagram.
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FIGURE 9-63 Floor counter state diagram.
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FIGURE 9-64 Elevator controller logic diagram.
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FIGURE 9-65
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FIGURE 9-66
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FIGURE 9-67
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FIGURE 9-68
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FIGURE 9-69
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FIGURE 9-70
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FIGURE 9-71
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FIGURE 9-72
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FIGURE 9-73
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FIGURE 9-74
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FIGURE 9-75
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FIGURE 9-76
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FIGURE 9-77
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FIGURE 9-78
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FIGURE 9-79
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FIGURE 9-80
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FIGURE 9-81
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FIGURE 9-82
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FIGURE 9-83
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TABLE 9–14
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FIGURE 9-84
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FIGURE 9-85