Sequential Logic Flip-Flop Circuits By Dylan Smeder

What Is A Sequential Circuit? Circuit that has memory Circuit that has memory Sequence of inputs creates memory Sequence of inputs creates memory At the simplest a Flip-Flop circuit At the simplest a Flip-Flop circuit “Sequential Circuits along with combinational circuits are the building blocks of computers” “Sequential Circuits along with combinational circuits are the building blocks of computers”

Simple memory Flip-Flop circuits have the ability to store 1 bit integers which is represented by either 1 or 0 Flip-Flop circuits have the ability to store 1 bit integers which is represented by either 1 or 0 The output of an operation is used as input for the next operation The output of an operation is used as input for the next operation The truth table is affected by memory instead of having one set of output for a set of input there are two different sets of output The truth table is affected by memory instead of having one set of output for a set of input there are two different sets of output

SR Flip-Flop Simple Flip-Flop circuit Simple Flip-Flop circuit Two inputs “S” and “R” Two inputs “S” and “R” S = Set S = Set R= Reset R= Reset Two outputs which are the complements of each other Q and Q’ Two outputs which are the complements of each other Q and Q’ Truth table has strange output Truth table has strange output

If S==1 and R==1 Q=0 and Q’=1 then Case A Q is 0 NOR 0 which equals 1 If S==1 and R==1 Q=0 and Q’=1 then Case A Q is 0 NOR 0 which equals 1 Cases A B C are similar to A Cases A B C are similar to A Case D and E are different. Each depends on the previous output. If in the previous output Q==0 and Q’==1 Case D and E are different. Each depends on the previous output. If in the previous output Q==0 and Q’==1 then Q=1 and Q’=0 If Q==1 and Q’==0 then Q=0 and Q’=1 If Q==1 and Q’==0 then Q=0 and Q’=1 How does a SR Flip-Flop work?

Clocked D Flip-Flop Variation of a SR Circuit Variation of a SR Circuit Can be set with a single input Can be set with a single input Pulse input CK Pulse input CK D input D input

How does Clocked D Flip-Flop 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 inputted in to the SR circuit When CP equals 1 D and its complement are inputted in to the SR circuit

Clocked JK Flip-Flop Variation of a Clocked D Flip-Flop Circuit Variation of a Clocked D Flip-Flop Circuit When CP equals 0 input from K and J are Ignored When CP equals 0 input from K and J are Ignored When CP equals 1 if K=J=1 it sets if in reset it resets if in set When CP equals 1 if K=J=1 it sets if in reset it resets if in set

Edge Detection 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 1 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 1 Edge detection only records theses changes Edge 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 triggered If it records a positive edge it is called a positive edge triggered If it records a negative edge it is called a negative edge triggered If it records a negative edge it is called a negative edge triggered

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

Random-Access Memory Can read and write at any point in memory Can read and write at any point in memory Implemented using D Flip-Flops Implemented using D Flip-Flops Each row contains 16 Flip-Flops Each row contains 16 Flip-Flops A Decoder A Decoder

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

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

Clocks and Sequencers To perform operations a CPU often requires a specific sequence of sub operations To perform operations a CPU often requires a specific sequence of sub operations A sequencer is used to make sure operations happen in correct order A sequencer is used to make sure operations happen in correct order A clock is a circuit that outputs 0’s and 1’s at specific frequencies A clock is a circuit that outputs 0’s and 1’s at specific frequencies

Real World Application The RAM discussed is a model for a chip that can actually be found in a computer The RAM discussed is a model for a chip that can actually be found in a computer The binary counter can be bought at tronics.com/webtronics/74hc161n.ht ml for 45 cents each The binary counter can be bought at tronics.com/webtronics/74hc161n.ht ml for 45 cents each tronics.com/webtronics/74hc161n.ht ml tronics.com/webtronics/74hc161n.ht ml The Flip-Flop circuits are models of usable chips The Flip-Flop circuits are models of usable chips

Sources flipflops/ flipflops/ flipflops/ flipflops/ tronics.com/webtronics/74hc161n.html tronics.com/webtronics/74hc161n.html tronics.com/webtronics/74hc161n.html tronics.com/webtronics/74hc161n.html Assembly language and computer architecture using C++ and JAVA, Anthony J Dos Reis, 2004 Assembly language and computer architecture using C++ and JAVA, Anthony J Dos Reis, 2004