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Sequential Logic

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

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Sequential Logic

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  1. Sequential Logic Flip-Flop Circuits By Dylan Smeder

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

  3. Simple memory • 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 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

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

  5. How does a SR Flip-Flop work? • 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 • 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

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

  7. How does Clocked D Flip-Flop Circuit Work? • 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

  8. Clocked JK Flip-Flop • Variation of a Clocked D Flip-Flop Circuit • 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

  9. 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 • Edge detection only records theses changes • Effectively levels out oscillations • 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

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

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

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

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

  14. Clocks and Sequencers • 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 clock is a circuit that outputs 0’s and 1’s at specific frequencies

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

  16. Sources • http://www.wearcam.org/ece385/lectureflipflops/flipflops/ • http://www.web-tronics.com/webtronics/74hc161n.html • Assembly language and computer architecture using C++ and JAVA, Anthony J Dos Reis, 2004

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