5.3 Sequential Circuits - An Introduction to Informatics WMN Lab. Hey-Jin Lee

outline Computer Organization Euclid’s Algorithm Sequential Circuits –Shift Registers –Sequential Adder –Counters Sequential Circuit Design 2

Computer Organization s d d d d d Storage Cell Addressing 0000~9999 [ Instruction set ] operand operation code Console Input / Output Arithmetic Unit AC Control Unit IC Figure Computer Organization ….. Storage Unit …… 3

Euclid’s Algorithm Address InstructionRemarks 1.Compute remainder AC ← m AC ← AC – n (r - n) Transfer if ( r – n ) < Transfer back to Add n back in. 2. Test for termination Go to end if r = Store result in r. 3. Replace m by n and n by r AC ← n m ← AC AC ← r n ← AC Return to main loop Halt. Answer is in n. … … … Value of m Value of n Initial value of r Figure 1-23 : The Complete gcd Program 4

Sequential Circuits What is the Sequential Circuits? –Circuit interconnected with combinational circuit and storage elements. –State Machine Storage Elements –Circuit capable of storing binary information representing the state of the sequential circuits. 5 Combinational Circuit n inputm output Storage Element Present states Next states Flip- Flop Clock pulses

Shift registers One important class of sequential circuits. For example Algoric If Shift then begin for i := 0 upto 2 do X[ i ] := X[ i+1 ]; x[3] := 0 end 6 Figure 5-9 : Shift Register FF FF FF FF Shift 1001

Sequential Adder 7 Figure 5-10 : Sequential Adder Block Diagram Figure 5-11 : Sequential Adder Algorithm Augend X, addend Y, and sum Z, the sum Z = X + Y can be obtained with a single one-bit full adder (FA) and a flip-flop to store a carry bit. Figure 5-11 : Sequential Adder Algorithm

Counters This procedure can be generalized to implement ANY finite state machine Counters are a very simple way to start: –no decisions on what state to advance to next current state is the output 8

Sequential Circuit Design Step 1: Making a state table. Step 2: Assigning binary codes to states. at least [ log 2 n ] digits  at least [ log 2 n ] flip-flops. Step 3: Finding flip-flop input values. Step 4: Find simplified equations for the flip-flop inputs and the outputs. Step 5: Build the circuit! For example  Recognizing a String of three One’s 9

Sequential Circuit Design Step 1: Making a state table. Input string : Output : input/output present state next state Step 1: Making a state table. Input string : Output : Figure 5-16 State Transition Graph Present StateInput Next StateOutput Start0 0 1One0 1Two0 1Start1 0 0 Two0Start0 Not used0X0 0x0

Sequential Circuit Design Step 2: Assigning binary codes to states. 11 State Transition Table

Sequential Circuit Design Step 3: Finding flip-flop input values. Use D flip-flop –You can just use the Next State columns 12

Sequential Circuit Design Step 4: Find simplified equations for the flip-flop inputs and the outputs. D A = A’ B I D A = B I D B = A’ B’ I O = A B’ I O=A B’ I + A B I =A I 13

Sequential Circuit Design Step 5: Build the circuit! D A = A’ B I D A = B I D B = A’ B’ I O = A B’ I O = A B’ I + A B I = A I 14 Figure 5-18 Recognizing Strings of Three One’s

Q & A 15 Thank you.