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C.S. Choy1 SEQUENTIAL LOGIC A circuit’s output depends on its previous state (condition) in addition to its current inputs The state of the circuit is kept in memory devices The state dependency is accomplished by feedback path

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C.S. Choy2 LATCH Active Low

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C.S. Choy3 LATCH Active High

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C.S. Choy4 LATCH APPLICATION Switch Debounce Almost all mechanical switches have contact bounce problem

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C.S. Choy5 GATED-LATCH Also known as level-triggered S-C Type D-Type

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C.S. Choy6 EDGED-TRIGGERED FLIP-FLOP D-Type

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C.S. Choy7 Positive-Edge Detector Negative-Edge Detector

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C.S. Choy8 D-TYPE FLIP-FLOP VARIATIONS Negative-Edge Triggered With Asynchronous Controls

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C.S. Choy9 TOGGLE FLIP-FLOP The flip-flop changes states on every active clock transition From the waveform, one can observe that when a toggle flip- flop is continuously driven by a clock signal of frequency f in, the output (Q) produces a repetitive waveform of frequency f out =f in /2 Divide-By-2 Circuit

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C.S. Choy10 J-K FLIP-FLOP

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C.S. Choy11 J-K FLIP-FLOP WITH MASTER-SLAVE CONFIGURATION

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C.S. Choy12 COMMON SEQUENTIAL CIRCUITS Counters A digital counter is a circuit used to generate binary numbers in a specific count sequence. That sequence is mainly governed by input clock pulses, and it is repetitive as long as these clock pulses are applied. Counters serve two main functions in digital systems – counting and frequency division ASYNCHRONOUSSYNCHRONOUS

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C.S. Choy13 ASYNCHRONOUS COUNTER (RIPPLE COUNTER) Basic building block is a toggle flip-flop Since each flip-flop receives its clock pulse from another flip- flop, there will be delay through these flip-flops. This addition delay is the longest for the MSB flip-flop

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C.S. Choy14 ALTERNATIVE MOD-8 UP-COUNTER

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C.S. Choy15 MOD-16 UP-COUNTER

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C.S. Choy16 COUNTERS OF OTHER MODULUS Mod-5

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C.S. Choy17 MISCOUNTS IN ASYNCHRONOUS COUNTER The additive propagation delays produce short duration of miscounts

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C.S. Choy18 MAXIMUM CLOCK FREQUENCY ALLOWED IN ASYNCHRONOUS COUNTERS n – number of stages ff – propagation delay of flip-flop

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C.S. Choy19 SYNCHRONOUS COUNTERS All flip-flops are clocked simultaneously Mod-16 Synchronous Up-Counter

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C.S. Choy20 MOD-10 SYNCHRONOUS UP-COUNTER (BCD OR DECADE) QA – toggle every time QB – toggle at A high and D low QC – toggle at A and B high QD – change high at A, B and C high but change low afterwards (A high)

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C.S. Choy21 MOD-8 DOWN COUNTER

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C.S. Choy22 MOD-8 SYNCHRONOUS UP/DOWN COUNTER

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C.S. Choy23 PRESETABLE COUNTERS

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C.S. Choy24 SYNCHRONOUS COUNTER DESIGN Mod-6 Up-Counter Using D-flip-flops –Design table

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C.S. Choy25 MOD-6 UP-COUNTER –K-maps –Final design

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C.S. Choy26 REGISTERS A group of latches or flip-flops used to store, transfer, or shift data Serial Shift Register Data is clocked into the register bit by bit It is important to note that level-triggered type of latches will not work properly

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C.S. Choy27 AN UNIVERSAL REGISTER S1S1 S0S0 Mode of operation 11Parallel load 10Shift left 01Shift right 00Hold

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C.S. Choy28 RING COUNTER The counter is a shift register that has its output connected back to its own input

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C.S. Choy29 JONHSON COUNTER Each bit is toggled in turn Mod-6 000 100 110 111 011 001 000 With its unique bit pattern, any sequence can be detected with a 2-input gate

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C.S. Choy30 MULTIPLY/DIVIDE REGISTER A left shift operation multiplies a binary number by a factor of 2 A right shift operation divides a binary number by a factor of 2

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C.S. Choy31 PSEUDO-RANDOM-SEQUENCE GENERATOR QAQA QBQB QCQC QDQD 0000 1000 0100 0010 1001 1100 0110 1011 0101 1010 1101 1110 1111 0111 0011 0001 1000 INVALID CONDITION

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