Sequential Circuit Design PDF

Sequential Circuit Design MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 1 Sequential Logic Design Contents Why sequential logic? Flip-flop criteria table Sequential circuit analysis Sequential circuit design MOHD. YAMANI IDRIS/ NOORZAILY M...

Sequential Circuit Design MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 1 Sequential Logic Design Contents Why sequential logic? Flip-flop criteria table Sequential circuit analysis Sequential circuit design MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 2 Why Sequential Logic? Sequential circuit has additional dimension which is time Combinational logic only depends on current input Sequential circuit output depends on previous input other than current input More powerful than combination logic Able to model condition which can’t be modeled by combinational logic MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 3 Sequential Circuit Analysis Given sequential circuit diagram, behavioral analysis from state table and also state diagram Need state equations to get flip-flop input and output functions for circuit output other than flip- flop (if any) We use A(t) and A(t+1) to represent current condition and the next condition for flip-flop represented by A. Other method, we can use A and A+ to represent current condition and the following condition MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 4 Sequential Circuit Analysis Example 1 (using D flip-flop) State equation Output Function MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 5 Sequential Circuit Analysis From the state equations and output function, we can derive state table which contains all combined binary available for current condition and input State table  The same as Truth Table  Input and condition pad on the left  Output and next condition on the right  combined binary available for current condition and input M flip-flop and n input => 2m+n line MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 6 Sequential Circuit Analysis State equation Output function State table for circuit in Example 1 MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 7 Sequential Circuit Analysis Other method MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 8 Sequential Circuit Analysis From the truth table, we can draw state diagram State diagram  Each state is represented by circle  Each arrow (between two circle) represent transfer for sequential logic (i.e. line transition in truth table)  a/b label for each arrow where a represent inputs and b represent output for circuit in transition Each flip-flop value combination represent state. Therefore, m flip-flop=> until 2m state. MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 9 Sequential Circuit Analysis State diagram for circuit in example 1 MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 10 Flip-flop Input Function Output of sequential circuit is a function of current condition for flip-flop and input. This is explained using algebra by circuit output function  In example 1: y= (A+B)x’ Circuit part that generate input to flip-flop is explained using algebra by flip-flop input functions MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 11 Flip-flop Input Function Flip-flop input function determine next condition From flip-flop input function and criteria table for flip-flop, we get next condition of the flip- flop MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 12 Flip-flop Input Function Example 2: circuit with JK flip flop We use 2 character to represent flip-flop input: first character represent flip-flop input (J or K for JK flip-flop, S or R for SR flip-flop, D for D flip-flop, T for T flip-flop ) and second character represent name of the flip-flop MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 13 Analysis: Example 3 Given sequential circuit with two JK flip-flop, A and B and one input x Get the input flip-flop function from the circuit MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 14 Analysis: Example 3 Input flip-flop function Fill the state table with the above function using criteria table for used flip-flop MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 15 Analysis: Example 3 Draw state diagram from the state table MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 16 Flip-flop Excitation Tables Analysis: Start from circuit diagram, build state table or state diagram Design: Start from specification set (i.e. in state equation form, state table or state diagram) build logic circuit. Criteria table is used in analysis Excitation tables is used in design MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 17 Flip-flop Excitation Tables Excitation tables : it give transition characteristic between current condition and next condition to determine flip-flop input MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 18 Designing Sequential Circuit Design steps Start with circuit spesification – characteristic of circuit Build state table Do state reduction if needed (not in syllabus) Do state assignment (not in syllabus) Determine number of flip-flop which will be used Build circuit excitation and output table from state table Build circuit output function and flip-flop input function Draw logic diagram MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 19 Design: Example 1 Given state diagram as follows, get the sequential circuit using JK flip-flop MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 20 Design: Example 1 State/excitation table using JK flip-flop MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 21 Design: Example 1 Block diagram MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 22 Design: Example 1 From state table, get input flip-flop function MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 23 Design: Example 1 Input flip-flop function Logic Diagram MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 24 Design: Example 2 Design, using D flip-flop, circuit is based on state table below. (Exercise: How if using JK flip-flop) MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 25 Design: Example 2 Determine input expression for flip-flop and y output MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 26 Design: Example 2 From expression built, draw logic diagram MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 27 Design a Synchronous Counter Counter: sequential circuit cycle through state sequence Binary counter: follow binary sequence. n-bit binary counter (with n flip-flop) able to count from 0 to 2n-1. Example 1: 3-bit binary counter (using T flip-flop) MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 28 Design a Synchronous Counter 3-bit binary counter (cont) MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 29 Design a Synchronous Counter 3-bit binary counter (cont) MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 30