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Objectives:•1 Define sequential logic circuit.•2 Differentiate between combinational logic circuit and sequential logic circuit.•3 Describe flip - flop.•4 Identify various types of flip-flops.•5 Build SR, JK, T and D flip – flop using logic gates.•6 Draw the symbol and truth table of SR, JK, T and D flip – flop. 2
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Sequential & Combinational logic circuit1 Define sequential logic circuit.2 Differentiate between combinational logic circuit and sequential logic circuit. 3
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Difference betweenCombinational & Sequential logic circuit Combinational Logic Circuits Basic building blocks include: Sequential Logic Circuits Basic building blocks include FLIP-FLOPS: 4
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Sequential S C Q logic circuit R Q• Sequential logic is the type of digital system that does not only depend on current input, but also the previous history of the system.• For that reason sequential logic requires memory elements to function.• The building blocks used to construct devices that store data are called flip-flops. 5
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Sequential logic circuit Sequential circuit have loops– these enable curcuits to receive feedback 6
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Combinational logic circuit• Combinational logic is an interconnection of logic gates to generate a specificities logic function where the inputs result in an immediate output, having no memory or storage capabilities.• There are function only based on their inputs, and NOT based on clocks. 7
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Combinational logic circuitCombinational circuit is combination of various logic gates 8
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Flip-Flop• "Flip-flop" is the common name given to two-state devices which offer basic memory for sequential logic operations.• Flip-flops are heavily used for digital data storage and transfer and are commonly used in banks called "registers" for the storage of binary numerical data. 10
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Flip-Flop• Flip-flop are basic storage/memory elements.• Flip-flop are essentially 1-bit storage devices.• Types of flip-flops are: • 1. SR Flip-flop • 2. JK Flip-flop • 3. D Flip-flop • 4. T Flip-flop• Application of flip-flop: • 1. Counter 4. Logic controller • 2. Register 5. Frequency Divider • 3. Memory 11
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SR Flip-Flop4 Identify various types of flip-flops.5 Build SR, JK, T and D flip – flop using logic gates.6 Draw the symbol and truth table of SR, JK, T and D flip – flop. 12
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SR Flip-Flop S Q R Q• The simplest binary storage device.• SR Flip-flop have 2 inputs (SET & RESET) and 2 outputs (Q & Q’). NOTE: Q & Q’ are compliments of each other• The SR flip flop is sometimes referred to as an SR latch. The Term latch refers to its use as a temporary memory storage device. 13
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SR Flip-Flop Symbol:SR Flip-flop (Active HIGH) SR Flip-flop (Active HIGH) NOR gate Symbol 14
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SR Flip-Flop Symbol:SR Flip-flop (Active LOW) SR Flip-flop (Active LOW) NAND gate Symbol 15
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SR Flip-Flop Truth Table:S R Q Q No change. Latch S Q0 0 NC NC remained in present state.1 0 1 0 Latch SET. R Q0 1 0 1 Latch RESET. SR Flip-flop1 1 0 0 Invalid condition. (Active HIGH)S R Q Q No change. Latch S Q1 1 NC NC remained in present state.0 1 1 0 Latch SET. R Q1 0 0 1 Latch RESET. SR Flip-flop0 0 1 1 Invalid condition. (Active LOW) 16
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IQ Test! What is the mode of operation of the SR flip-flop (set, reset or hold)? What is the output at Q from the SR flip-flop (active LOW inputs)? L ? High H Mode of operation = Set ? H ? High H Mode of operation = Hold ? H ? Low L Mode of operation = ? Reset 18
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Clock SR Flip-Flop4 Identify various types of flip-flops.5 Build SR, JK, T and D flip – flop using logic gates.6 Draw the symbol and truth table of SR, JK, T and D flip – flop. 19
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Clock• Flip-flops: synchronous bistable devices• Output changes state at a specified point on a triggering input called the clock.• Change state either at the positive edge (rising edge) or at the negative edge (falling edge) of the clock signal. Clock signal Positive Negative edges edges 20
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Clock SR Flip-Flop• The Clocked SR Flip Flop like SR flip-flop but with extra third input of a standard clock pulse.• The output of Q and NOT Q will not change (despite making changes to the inputs Set & Reset) in a Clocked RS Flip-flop Until receiving a signal from the clock. 21
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Clock SR Flip-Flop Symbol:Clock SR Flip-flop (+ve EDGE) Clock SR Flip-flop (+ve EDGE)Combination gate Symbol 22
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Clock SR Flip-Flop Truth Table:• S-R flip-flop: on the triggering edge of the clock pulse,• S=HIGH and R=LOW is a SET state• R=HIGH (and S=LOW) is a RESET state• If both SR inputs LOW a NO change• If both SR inputs HIGH a INVALID• Truth table of positive edge-triggered S-R flip-flop: S R CLK Q(t+1) Comments X = irrelevant (“don’t care”) 0 0 X Q(t) No change = clock transition LOW to HIGH 0 1 0 Reset 1 0 1 Set 1 1 ? Invalid 24
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Clock SR Flip-Flop Timing Diagram:How if we add clock as input? Please draw the output waveform for me (Positive edge triggered) 25
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D Flip-Flop4 Identify various types of flip-flops.5 Build SR, JK, T and D flip – flop using logic gates.6 Draw the symbol and truth table of SR, JK, T and D flip – flop. 26
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D Flip-Flop D Q Truth Table: C Q• D flip-flop: single input D (data)• D=HIGH a SET state• D=LOW a RESET state• Q follows D at the clock edge.• D flip-flop formed by add NOT gate between SR input. D S Q D CLK Q(t+1) CommentsCLK C 1 1 Set R Q 0 0 Reset = clock transition LOW to HIGH 27
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D Flip-Flop Symbol: D QCLK Q D Flip-flop (+ve EDGE) D Flip-flop (+ve EDGE) Combination gate Symbol 28
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D Flip-Flop Timing Diagram:CLKCLK CLK CLK Q Q’ 29
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JK Flip-Flop4 Identify various types of flip-flops.5 Build SR, JK, T and D flip – flop using logic gates.6 Draw the symbol and truth table of SR, JK, T and D flip – flop. 30
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JK Flip-Flop J C Q K Q• J-K flip-flop: Q and Q are feedback to the pulse- steering NAND gates.• No invalid state.• Include a toggle state. • J=HIGH (and K=LOW) a SET state • K=HIGH (and J=LOW) a RESET state • If both inputs LOW a NO change • If both inputs HIGH a Toggle 31
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JK Flip-Flop Symbol: J QCLK Q K JK Flip-flop (+ve EDGE) JK Flip-flop (+ve EDGE) Combination gate Symbol 32
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JK Flip-Flop Truth Table:J K CLK Q(t+1) Comments0 0 Q(t) No change0 1 0 Reset1 0 1 Set1 1 Q(t) Toggle 33
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JK Flip-Flop Application: Frequency Division High High High J J QA J QB Q CLK C CLK C C K K KCLK CLK Q QA QB Divide clock frequency by 2. Divide clock frequency by 4. 34
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JK Flip-Flop Timing Diagram:Similar to S-R flip-flop but toggles when J = K = 1 35
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T Flip-Flop4 Identify various types of flip-flops.5 Build SR, JK, T and D flip – flop using logic gates.6 Draw the symbol and truth table of SR, JK, T and D flip – flop. 36
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T Flip-Flop T J Q Truth Table: CLK C K Q • T flip-flop: single-input version of the J-K flip flop, formed by tying both inputs together.T T CLK Q(t+1) Comments Q 0 Q(t) No change CLK 1 Q(t) Toggle Q 37
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