Post on 14-Apr-2017
transcript
DIGITAL ELECTRONICS
RC1225_013Nandhini V. L (Team Leader)Kusuma M.S.
Digital Electronics is a branch of Electronics deals with the digital circuits and digital signals.
BasicsCombinational CircuitsSequentional Circuits
BASIC GATES
Digital Computers store the data in Binary format that is in terms of logic ‘0’ and logic ‘1’.
Basic logic block –GATE
BinaryDigitalInputSignal
BinaryDigitalOutputSignal
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 previous state of the blocks
Functions of Gates can be described by
- Truth Table - Boolean Function - Karnaugh Map
BASIC CONCEPTS Simple gates
AND OR NOT
Functionality can be expressed by a truth table A truth table lists output
for each possible input combination
Precedence NOT > AND > OR F = A B’ + A’ B = (A (B’)) + ((A’) B)
Additional useful gates
Universal gates NAND NOR
NAND = AND + NOT NOR = OR + NOT Additional gate: XOR gate XOR implements
exclusive-OR function NAND and NOR gates
require only 2 transistors AND and OR need 3 transistors
COMBINATIONAL CIRCUITS
Output depends only on the present inputs. Combinational circuits provide a higher level of
abstraction.Help in reducing design complexity.Reduce chip count.
We look at some useful combinational circuits
COMBINATIONAL LOGIC CIRCUITS
Half AdderFull Adder Multiplexer
Encoder Decoder Parity Checker Parity Generator etc
ADDERS
Half-adderAdds two bits
Produces a sum and carry
Full-adderAdds three 1-bit values
Like half-adder, produces a sum and carryAllows building N-bit adders
Simple techniqueConnect Cout of one adder to Cin of the next
These are called ripple-carry adders
a sumb carr
y
Coutsum
Cin
ab
HA
FA
MULTIPLEXER
2n data inputs n selection inputs a single output
Selection input determines the input that should be connected to the output
Multiplexers(Continued…)
4-data input MUX implementation
Multiplexers(Continued…)
4-data input MUX
Multiplexers(Continued…)
Example chip: 8-to-1 MUX
Demultiplexer (DeMUX)
DEMULTIPLEXERS
Decoders
Decoder selects one-out-of-N inputs
Comparator
Used to implement comparison operators (= , > , < , , )
Comparator (cont.) A=B: OX = IX (X=A<B, A=B, & A>B)
4-bit magnitude comparator chip
Thank you