# Journey to Work

Topics: Digital, Binary numeral system, Flip-flop Pages: 16 (2298 words) Published: January 8, 2013
Digital Fundamentals
with PLD Programming
Floyd

Chapter 1

Floyd, Digital Fundamentals, 10th ed

Summary
Analog Quantities Most natural quantities that we see are analog and vary continuously. Analog systems can generally handle higher power than digital systems. Temperature ( F) 100 95 90 85 80 75 70 Time of day 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 A .M .

5 6 7 8 9 10 11 12
P.M .

Digital systems can process, store, and transmit data more efficiently but can only assign discrete values to each point. Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved

Summary
Analog and Digital Systems Many systems use a mix of analog and digital electronics to take advantage of each technology. A typical CD player accepts digital data from the CD drive and converts it to an analog signal for amplification. CD drive

10110011101 Digital data

Digital-to-analog converter

Linear amplifier Analog reproduction of music audio signal

Speaker Sound waves

Floyd, Digital Fundamentals, 10th ed

Summary
Binary Digits and Logic Levels Digital electronics uses circuits that have two states, which are represented by two different voltage levels called HIGH and LOW. The voltages represent numbers in the binary system. VH(max) VH(min)

In binary, a single number is called a bit (for binary digit). A bit can have the value of either a 0 or a 1, depending on if the voltage is HIGH or LOW.

HIGH

Invalid
VL(max)

LOW
VL(min)

Floyd, Digital Fundamentals, 10th ed

Summary
Digital Waveforms Digital waveforms change between the LOW and HIGH levels. A positive going pulse is one that goes from a normally LOW logic level to a HIGH level and then back again. Digital waveforms are made up of a series of pulses. HIGH Rising or leading edge LOW t0 t1 Falling or trailing edge HIGH Falling or leading edge LOW t0 t1 Rising or trailing edge

(a) Positive–going pulse

(b) Negative–going pulse

Floyd, Digital Fundamentals, 10th ed

Summary
Pulse Definitions Actual pulses are not ideal but are described by the rise time, fall time, amplitude, and other characteristics. Overshoot Ringing Droop 90% Amplitude 50% 10% Base line tr Rise time tf Fall time tW Pulse width Ringing Undershoot

Floyd, Digital Fundamentals, 10th ed

Summary
Periodic Pulse Waveforms Periodic pulse waveforms are composed of pulses that repeats in a fixed interval called the period. The frequency is the rate it repeats and is measured in hertz. f 1 T

T

1 f

The clock is a basic timing signal that is an example of a periodic wave. What is the period of a repetitive wave if f = 3.2 GHz?
T
Floyd, Digital Fundamentals, 10th ed

1 f

1 3.2 GHz

313 ps

Summary
Pulse Definitions In addition to frequency and period, repetitive pulse waveforms are described by the amplitude (A), pulse width (tW) and duty cycle. Duty cycle is the ratio of tW to T. Volts

Amplitude (A)

Pulse width (tW)

Time
Period, T

Floyd, Digital Fundamentals, 10th ed

Summary
Timing Diagrams A timing diagram is used to show the relationship between two or more digital waveforms, Clock

A B C

A diagram like this can be observed directly on a logic analyzer. Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved

Summary
Serial and Parallel Data Data can be...