BTEC NC - Electronics - Combinational and Sequential Logic Circuits

8/2/2019 BTEC NC - Electronics - Combinational and Sequential Logic Circuits

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Brendan Burr BTEC National Certificate in ElectronicsCombinational & Sequential Logic Circuits

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Task 1Input A Input B Output U

0 0 10 1 1

1 0 11 1 0

Logic Function NAND

Input A Input B Output V0 0 00 1 01 0 01 1 1

Logic Function AND

Input A Output W0 11 0

Logic Function NOT

Input A Input B Output X0 0 00 1 11 0 11 1 1

Logic Function OR

Input A Input B Output Y0 0 10 1 01 0 01 1 0

Logic Function NOR

Input A Input B Input C Output Z0 0 0 00 0 1 10 1 0 0

0 1 1 11 0 0 01 0 1 11 1 0 11 1 1 1

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Task 2 The circuit is Asynchronous, this is because the clock of the next flipflop is determined by the Q output of the previous flip flop.

Flip Flop Mode of Operation ToggleSynchronous or Asynchronous Asynchronous

Clock Pulse C B A0 0 0 01 0 0 12 0 1 03 0 1 14 1 0 0

5 1 0 16 1 1 07 1 1 18 0 0 09 0 0 1

Why a Binary Counter? To divide the periodic cycle by two or add oneNo. of Clock Pulses in Output A? 4No. of Clock Pulses in Output B? 4No. of Clock Pulses in Output C? 4Maximum decimal number? 7

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Task 3

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Task 4

Ne w Truth Table

Input C Input B Input A U V W X Y Z0 0 0 1 0 1 0 1 00 0 1 1 0 0 1 0 00 1 0 1 0 1 1 0 00 1 1 0 1 0 1 0 11 0 0 1 0 1 0 1 11 0 1 1 0 0 1 0 11 1 0 1 0 1 1 0 11 1 1 0 1 0 1 0 1

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Task 5CMOS 4000 Series 74LS TTL

Propagation Delay (Speed) 125nS at 5 Volts 10nS at 5 Volts 60nS at 10 Volts

45nS at 15 VoltsSupply Voltage 3-15 Volts 5 VoltsInput Voltage Level - Logic High 3.5 Volts 2 VoltsInput Voltage Level - Logic Low 1.5 Volts 0.8 VoltsOutput Voltage Level - Logic High 4.95 Volts 2.4 VoltsOutput Voltage Level - Logic Low 0.05 Volts 0.4 VoltsSource Current 6.8 mA 16 mASink Current 0.5 mA 1.6 mA

The are a many differences between the 74LS TTL and the CMOS4000 Series Integrated Chips, this is clearly represented on the table

above. The basic information shows that the 74LS TTL chips require alower supply voltage, however the CMOS 4000 Series chips can bevaried, depending on the Propagation Delay required. At the samesupply voltage the TTL chip is clearly much faster than the CMOSchip.

Propagation Delay The amount of time it takes for a digital signalto pass through a logic gate from the input and reach its output.Supply Voltage The range of voltage that is required to maintainthe component in a working state.Input Voltage Level Logic High The electronic representation

of logic high is 1. A logic high is above 2 volts for the 74LS TTL chip.Input Voltage Level Logic Low The electronic representation of logic low is 0. A logic low is less than 0.8 volts for the 74LS TTL chip.Output Voltage Level Logic High With the output logic at 1 theoutput voltage needs to be 2.4 volts or above. The output seems tohave a gain from the input which suggests amplification. Transistorscan be used for amplification, and the TTL stands for Transistor

Transistor Logic.Output Voltage Level Logic Low With the output logic at 0 theoutput voltage needs to be 0.4 volts or below.Source Current The source current is the amount of current that isrequired to allow the chips to run. It is the amount of current that isvisible when on a positive cycle.Sink Current The sink current is the amount of current that bleedsaway from the device, which is not visible.

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BTEC NC - Electronics - Combinational and Sequential Logic Circuits

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