DIGITAL LOGIC CIRCUITS

1. Introduction DIGITAL LOGIC CIRCUITS Logic Gates Boolean Algebra Map Specification Combinational Circuits Flip-Flops Sequential Circuits Memory Components

2. Logic Gates BASIC LOGIC BLOCK - GATE - Binary Digital Output Signal Binary Digital Input Signal Gate . . . Types of Basic Logic Blocks - Combinational Logic Block Logic Blocks whose output logic value depends only on the input logic values - Sequential Logic Block Logic Blocks whose output logic value depends on the input values and the state (stored information) of the blocks Functions of Gates can be described by - Truth Table - Boolean Function - Karnaugh Map

3. Logic Gates COMBINATIONAL GATES Name Symbol Function Truth Table A B X A X = A • B X or B X = AB 0 0 0 0 1 0 1 0 0 1 1 1 0 0 0 0 1 1 1 0 1 1 1 1 AND A B X A X X = A + B B OR A X I 0 1 1 0 A X X = A A X 0 0 1 1 Buffer A X X = A A B X A X X = (AB)’ B 0 0 1 0 1 1 1 0 1 1 1 0 NAND A B X A X X = (A + B)’ B 0 0 1 0 1 0 1 0 0 1 1 0 NOR A B X A X = A  B X or B X = A’B + AB’ XOR Exclusive OR 0 0 0 0 1 1 1 0 1 1 1 0 A B X A X = (A  B)’ X or B X = A’B’+ AB XNOR 0 0 1 0 1 0 1 0 0 1 1 1 Exclusive NOR or Equivalence

4. Boolean Algebra LOGIC CIRCUIT DESIGN x y z F 0 0 0 0 0 0 1 1 0 1 0 0 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 1 Truth Table Boolean Function F = x + y’z x F y Logic Diagram z

5. Boolean Algebra BASIC IDENTITIES OF BOOLEAN ALGEBRA [1] x + 0 = x [3] x + 1 = 1 [5] x + x = x [7] x + x’ = 1 [9] x + y = y + x [11] x + (y + z) = (x + y) + z [13] x(y + z) = xy +xz [15] (x + y)’ = x’y’ [17] (x’)’ = x [2] x • 0 = 0 [4] x • 1 = x [6] x • x = x [8] x • X’ = 0 [10] xy = yx [12] x(yz) = (xy)z [14] x + yz = (x + y)(x + z) [16] (xy)’ = x’ + y’ [15] and [16] : De Morgan’s Theorem

6. Boolean Algebra EQUIVALENT CIRCUITS Many different logic diagrams are possible for a given Function F = ABC + ABC’ + A’C .......…… (1) = AB(C + C’) + A’C [13] ..…. (2) = AB • 1 + A’C [7] = AB + A’C [4] ...…. (3) A B C (1) (2) (3) F A B C F A B C F

7. Boolean Algebra COMPLEMENT OF FUNCTIONS A,B,...,Z,a,b,...,z  A’,B’,...,Z’,a’,b’,...,z’ (p + q)  (p + q)’ - Replace all the operators with their respective complementary operators AND  OR OR  AND - Basically, extensive applications of the DeMorgan’s theorem (x1 + x2 + ... + xn )’  x1’x2’... xn’ (x1x2 ... xn)'  x1' + x2' +...+ xn'

8. Map Simplification SIMPLIFICATION Boolean Function Truth Table Many different expressions exist Unique Karnaugh Map(K-map) is a simple procedure for simplifying Boolean expressions. Truth Table Simplified Boolean Function Karnaugh Map Boolean function

9. Combinational Logic Circuits x y c s 0 0 0 0 0 1 0 1 1 0 0 1 1 1 1 0 x y c s COMBINATIONAL LOGIC CIRCUITS y y Half Adder 0 0 0 1 1 1 0 x 0 x c = xy s = xy’ + x’y = x  y Full Adder y y x y cn-1 cn s 0 1 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 0 1 0 1 1 1 0 1 0 0 0 1 1 0 1 1 0 1 1 0 1 0 1 1 1 1 1 1 0 0 1 cn-1 cn-1 0 1 1 1 x x 0 0 1 1 cn s cn = xy + xcn-1+ ycn-1 = xy + (x  y)cn-1 s = x’y’cn-1+x’yc’n-1+xy’c’n-1+xycn-1 = x  y  cn-1 = (x  y)  cn-1 x y S cn cn-1

10. Combinational Logic Circuits COMBINATIONAL LOGIC CIRCUITS Other Combinational Circuits Multiplexer Encoder Decoder etc

11. Combinational Logic Circuits Select Output S1 S0 Y 0 0 I0 0 1 I1 1 0 I2 1 1 I3 MULTIPLEXER 4-to-1 Multiplexer I0 I1 Y I2 I3 S0 S1

12. Combinational Logic Circuits D1 A0 D2 A1 D3 D4 D5 A2 D6 E A1 A0 D0 D1 D2 D3 D7 0 0 0 0 1 1 1 0 0 1 1 0 1 1 0 1 0 1 1 0 1 0 1 1 1 1 1 0 1 d d 1 1 1 1 ENCODER/DECODER Octal-to-Binary Encoder 2-to-4 Decoder D0 D1 A0 D2 D3 A1 E

13. Sequential Circuits SEQUENTIAL CIRCUITS - Registers A0 A1 A2 A3 Q Q Q Q C C C C D D D D Clock I0 I1 I2 I3 Shift Registers Serial Output Serial Input Clock D Q C D Q C D Q C D Q C Bidirectional Shift Register with Parallel Load A3 A1 A0 A2 Q Q Q Q C C C C D D D D 4 x 1 MUX 4 x 1 MUX 4 x 1 MUX 4 x 1 MUX Serial Input I3 I0 Clock S0S1 I1 I2 SeriaI Input

14. Memory Components n data input lines k address lines Read Write 2k Words (n bits/word) n data output lines MEMORY COMPONENTS 0 Logical Organization words (byte, or n bytes) N - 1 Random Access Memory - Each word has a unique address - Access to a word requires the same time independent of the location of the word - Organization

15. Memory Components READ ONLY MEMORY(ROM) Characteristics - Perform read operation only, write operation is not possible - Information stored in a ROM is made permanent during production, and cannot be changed

16. Question • The following memory units are specified by the number of words times the number of bits per word. How many address lines and input-output data lines are needed in each case? • (a)2K x 16. • (b)64M x 8. • (c)16G x 32.

17. Question • Specify the number of bytes that can be stored in the memories listed in he following memory units: • (a)2K x 16. • (b)64M x 8. • (c)16G x 32.

18. REPRESENTATION OF NUMBERS Decimal Binary Octal Hexadecimal 00 0000 00 0 01 0001 01 1 02 0010 02 2 03 0011 03 3 04 0100 04 4 05 0101 05 5 06 0110 06 6 07 0111 07 7 08 1000 10 8 09 1001 11 9 10 1010 12 A 11 1011 13 B 12 1100 14 C 13 1101 15 D 14 1110 16 E 15 1111 17 F Binary, octal, and hexadecimal conversion Octal 1 2 7 5 4 3 Binary 1 0 1 0 1 1 1 1 0 1 1 0 0 0 1 1 Hexa

19. Questions • Convert the following binary numbers to decimal: • 10011100 • 00110110 • Convert the following decimal numbers to binary : • 70 • 160 • Convert the following binary numbers to Hexadecimal: • 1100 1010 0011 • 0110 1000 1100 0000