Sequential LogicSequential Logic

Flip-Flop CircuitsFlip-Flop Circuits

By Dylan SmederBy Dylan Smeder

What Is A Sequential Circuit?What Is A Sequential Circuit?

Circuit that has memoryCircuit that has memory Sequence of inputs creates memorySequence of inputs creates memory At the simplest a Flip-Flop circuitAt the simplest a Flip-Flop circuit ““Sequential Circuits along with Sequential Circuits along with

combinational circuits are the combinational circuits are the building blocks of computers”building blocks of computers”

Simple memorySimple memory

Flip-Flop circuits have the ability to store 1 bit Flip-Flop circuits have the ability to store 1 bit integers which is represented by either 1 or 0integers which is represented by either 1 or 0

The output of an operation is used as input for The output of an operation is used as input for the next operationthe next operation

The truth table is affected by memory instead of The truth table is affected by memory instead of having one set of output for a set of input there having one set of output for a set of input there are two different sets of outputare two different sets of output

SR Flip-FlopSR Flip-Flop

Simple Flip-Flop circuitSimple Flip-Flop circuit Two inputs “S” and “R”Two inputs “S” and “R” S = Set S = Set R= ResetR= Reset Two outputs which are the complements of each other Q Two outputs which are the complements of each other Q

and Q’and Q’ Truth table has strange outputTruth table has strange output

If S==1 and R==1 Q=0 and Q’=1 then If S==1 and R==1 Q=0 and Q’=1 then Case A Q is 0 NOR 0 which equals 1Case A Q is 0 NOR 0 which equals 1

Cases A B C are similar to ACases A B C are similar to A Case D and E are different. Each depends Case D and E are different. Each depends

on the previous output. If in the previous on the previous output. If in the previous output Q==0 and Q’==1output Q==0 and Q’==1then Q=1 and Q’=0 then Q=1 and Q’=0

If Q==1 and Q’==0 then Q=0 and Q’=1If Q==1 and Q’==0 then Q=0 and Q’=1

How does a SR Flip-Flop How does a SR Flip-Flop work?work?

Clocked D Flip-FlopClocked D Flip-Flop

Variation of a SR CircuitVariation of a SR Circuit Can be set with a single inputCan be set with a single input Pulse input CKPulse input CK D inputD input

How does Clocked D Flip-Flop How does Clocked D Flip-Flop Circuit Work?Circuit Work?

When CP is equal to 0 the input from D is ignored When CP is equal to 0 the input from D is ignored When CP equals 1 D and its complement are When CP equals 1 D and its complement are

inputted in to the SR circuitinputted in to the SR circuit

Clocked JK Flip-FlopClocked JK Flip-Flop

Variation of a Clocked D Flip-Flop Variation of a Clocked D Flip-Flop CircuitCircuit

When CP equals 0 input from K and J When CP equals 0 input from K and J are Ignoredare Ignored

When CP equals 1 if K=J=1 it sets if When CP equals 1 if K=J=1 it sets if in reset it resets if in setin reset it resets if in set

Edge DetectionEdge Detection

With a single input there can be various signal levels but the With a single input there can be various signal levels but the only level needed is when it switches from 1 to 0 or 0 to 1only level needed is when it switches from 1 to 0 or 0 to 1

Edge detection only records theses changesEdge detection only records theses changes Effectively levels out oscillations Effectively levels out oscillations If it records a positive edge it is called a positive edge If it records a positive edge it is called a positive edge

triggered triggered If it records a negative edge it is called a negative edge If it records a negative edge it is called a negative edge

triggeredtriggered

T Flip-FlopT Flip-Flop

Positive edge triggered JK Flip-FlopPositive edge triggered JK Flip-Flop J and K inputs are tied togetherJ and K inputs are tied together Used as countersUsed as counters

Random-Access MemoryRandom-Access Memory

Can read and write at any point in Can read and write at any point in memorymemory

Implemented using D Flip-FlopsImplemented using D Flip-Flops Each row contains 16 Flip-Flops Each row contains 16 Flip-Flops A DecoderA Decoder

Binary CounterBinary Counter

Holds each pulse in memoryHolds each pulse in memory Each pulse add another number Each pulse add another number Binary format Binary format

RegisterRegister

Used to hold one item of informationUsed to hold one item of information CPU’s have many registers CPU’s have many registers AX is an example in AssemblyAX is an example in Assembly

Clocks and SequencersClocks and Sequencers

To perform operations a CPU often To perform operations a CPU often requires a specific sequence of sub requires a specific sequence of sub operations operations

A sequencer is used to make sure A sequencer is used to make sure operations happen in correct order operations happen in correct order

A clock is a circuit that outputs 0’s A clock is a circuit that outputs 0’s and 1’s at specific frequencies and 1’s at specific frequencies

Real World ApplicationReal World Application

The RAM discussed is a model for a The RAM discussed is a model for a chip that can actually be found in a chip that can actually be found in a computercomputer

The binary counter can be bought at The binary counter can be bought at http://www.web-tronics.com/webtronihttp://www.web-tronics.com/webtronics/74hc161n.htmlcs/74hc161n.html for 45 cents each for 45 cents each

The Flip-Flop circuits are models of The Flip-Flop circuits are models of usable chipsusable chips

SourcesSources

http://www.wearcam.org/ece385/lectureflipflops/flhttp://www.wearcam.org/ece385/lectureflipflops/flipflops/ipflops/

http://www.web-tronics.com/webtronics/74hc161nhttp://www.web-tronics.com/webtronics/74hc161n.html.html

Assembly language and computer architecture Assembly language and computer architecture using C++ and JAVA, Anthony J Dos Reis, 2004using C++ and JAVA, Anthony J Dos Reis, 2004