LOGIC12_r2 - Chapter 12 Counters Simular Sequential...

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Chapter 12 Counters & Simular Sequential Networks
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The counters discussed in this chapter are all synchronous. This means the operation of the FFs is synchronized by the common input pulse ( p ) so that when several FFs must change state, the state changes occur simultaneously.
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Ex: Binary counter using 3 TFFs to count pulses. Operation: Initially, all FFs will be set to the “0” state. (000) When a pulse is received, the counter will change to state 001; when a second pulse is received, the state will change to 001, etc. The sequence of FF states is ABC = 000, 001, 010, 011, 100, 101, 110, 111, 000,…… Note that when the counter reaches state 111, the next pulse resets it to the 000 state and then the sequence repeats.
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so, C changes every time when a pulse is sent B changes every time when C 1 a pulse a sent A changes every time when C 1, B 1 a pulse is sent
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Synchronous Binary Counter
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State Table Present state Next state FF Inputs A B C A + B + C + T A T B T C 0 0 0 0 0 1 0 0 1 0 0 1 0 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 1 0 0 1 1 1 1 0 0 1 0 1 0 0 1 1 0 1 1 1 0 0 1 1 1 1 0 1 1 1 0 0 1 1 1 1 0 0 0 1 1 1 A B C A + B + C + 與 與 與 與 與 與 與 FF 與 與 與 與
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T C 1 T B C T A BC T C P T B CP T A BCP A BC 0 1 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 A BC 0 1 0 0 0 0 0 1 0 0 1 1 1 1 1 0 0 0 A BC 0 1 0 0 1 1 0 1 1 1 1 1 1 1 1 0 1 1
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§ Counters for other sequences Ex The state graph for a counter
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1. Form a state table and treat the unspecified states as “don’t care terms” Present state Next state A B C A + B + C + 0 0 0 1 0 0 0 0 1 X X X 0 1 0 0 1 1 0 1 1 0 0 0 1 0 0 1 1 1 1 0 1 X X X 1 1 0 X X X 1 1 1 0 1 0
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2.
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LOGIC12_r2 - Chapter 12 Counters Simular Sequential...

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