Digital Electronics I: Overview of Basic Logic Functions and Combinational Circuits, Slides of Digital Electronics

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EEE130 Digital Electronics I

Lecture #1_2 Dr. Shahrel A. Suandi

1-4 Overview of Basic Logic

Functions

-^ Digital systems are generally built fromcombinations of NOT, AND and OR logicelements •^ The combinations of these elements can beused for the followings:^ – Comparison, arithmetic, codes conversion, encoding,

decoding, data selection, storage and

-^ This section will only give introduction to thesecommon logics, while the details will beexplained in future chapters (Chapter 6)

The Arithmetic Functions – Adder • What is arithmetic function?^ – Normal mathematical operations, like addition, subtraction,multiplication, division • Addition – to add numbers and known as

adder

• Add 2 numbers and generate two outputs, a sum and a carry

Subtractor, multiplier and divider •^ Subtractor is used for subtraction^ – Requires 3 inputs:

-^ 2 inputs •^ 1 borrow input -^ Multiplier is used for multiplication^ – Two inputs/numbers are multiplied at a time^ – Multiplication is actually a process of multiple time of addition, so

we can also use adder

for this purpose

-^ Divider is used for division^ – Two inputs/numbers are used for this purpose^ – The outputs generated are the quotient and the remainder^ – Similar to multiplier, divider is actually series of subtractions,

comparisons, and shifts

Æ^ adder can be used

in conjunction with

other circuits for this purpose

-^ Do you know ALU??–^

Arithmetic Logic Unit– a unit where allarithmetic operationsare done in amicroprocessor

The Encoding Function

-^ Encoder – converts information from one form to anotherform •^ Example:^ – Calculator: when button “9” is pressed, then the terminal is HIGH

and being as the input to an encoder. This number “9” is thenconverted into binary, for example “1001” (BCD)

The Decoding Function

•^ Decoder – performs decoding function •^ Example:^ – decode a binary number into a non-coded form, such

as a decimal form

The Storage Function

-^ Usage: to retain binary data for a period of time •^ Example of storage devices:^ –^

Flip-flops, registers, semiconductor memories, magnetic disks, magnetictape, and optical disks (CDs)

-^ Flip-flops – a bistable logic circuit that can store only one bit at atime, either 1 or 0 •^ Registers^ –^

a combination of several flip-flops forms registers, 8-bit register isconstructed from eight flip-flops – Shift registers are registers used to shift the bits from one position toanother within the register or out of the register to another circuit

-^ Semiconductor memories – used for storing large numbers of bits.E.g.: ROM (permanently or semipermanently stored), RAM(temporarily stored) •^ Magnetic memories – used for mass storage of binary data. E.g.:floppy disk

Examples of registers(1)^ - serial shift register -

The Counting Function

•^ As its’ name, the counter is used to count eventsrepresented by changing levels or pulses •^ Important characteristics: storage capabilities •^ Flip-flop are used to implement counting

1-5 Fixed Function Integrated

Circuit (IC) (1)

-^ Logic elements and functions can be found available in integrated circuit (IC) formbecause–^

Small size, high reliability, low cost, low power consumption

-^ Monolithic IC – an eletronic circuit that is constructed entirely on a single chip ofsilicon•^ Digital IC can be divided into 2:–^

Fixed-function logic – logic function have been fixed by the manufacturer. Need to refer specsheet before using it / cannot be changed– Programmable logic – logic function can be changed based on the program that we write intothe IC

-^ IC Packages–^

DIP (Dual In Line) – the most common– SMT (Surface Mount Technology) – eg. Small outline integrated circuit (SOIC), PLCC(Plastic leaded chip carrier), LCCC (Leadless ceramic chip carrier).– others: SSOP, TSSOP and TVSOP

1-6 Introduction to Programmable

Logic

-^ Types of Programmable Logic Devices–^

SPLD (Single Programmable Logic Device) – there are PAL and GAL– CPLD (Complex Programmable Logic Device)– FPGA (Field Programmable Gate Array)

PLD (ProgrammableLogic Device)

Programming Process

• Design Entry • Functional Simulation • Synthesis • Implementation • Timing simulation • Download

Block Diagram of Analog and

Digital Oscilloscopes

Other Equipments

• The Logic Analyzer • Signal Generator^ – Waveform generator, function generator • Others:^ – DC Power Supply