Digital Fundamentals Floyd Chapter 1 Digital concepts Tenth Edition © 2008 Pearson Education

Summary Digital and Analog Quantities Analog quantity is one having continuous values. Digital quantity is one having a discrete set of values.

Summary Digital and Analog Quantities Most natural quantities that we see are analog and vary continuously (For example Air Temperature). Analog systems can generally handle higher power than digital systems. Digital systems can process, store, and transmit data more efficiently but can only assign discrete values to each point.

Summary Digital and Analog Quantities

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.

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) 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 VH(min) Invalid VL(max) LOW VL(min)

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 to its LOW level . A Negative-going pulse generated when the voltage goes from its normally HIGH level to its LOW level and back to its HIGH level Digital waveforms are made up of a series of pulses.

Summary Pulse Definitions Pulse has two edges: Leading edge Occurs first at time t0 Trailing edge Occurs last at time t1 for a positive-going pulse the leading edge is a rising edge and Trailing edge is a falling edge Pulses ideal when the rising and falling edges are assumed to change in zero time (in-stantaneously)

Summary Pulse Definitions Rise time (tr) the time required for a pulse to go from its low level to its high level. Fall time (tf) the time required for a pulse to go from its high level to its low level. Amplitude height from baseline.

Summary Pulse Definitions Actual pulses are not ideal but are described by the rise time, fall time, amplitude, and other characteristics.

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 at which it repeats it self and is measured in hertz.

Summary Pulse Definitions In addition to frequency and period, repetitive pulse waveforms are described by the amplitude (A), pulse width (tW) and duty cycle. pulse width (tw) is a measure of the duration of the pulse Duty cycle is the ratio of pulse width (t)W to period (T). Pulse width (tW) Amplitude (A) Period, T

Summary Digital Waveform Carries Binary Information Bit time each bit in a sequence occupies a defined time interval. The clock is a basic timing signal that is an example of a periodic wave.

Summary Timing Diagrams A timing diagram is graph of digital waveforms showing the actual time relationship of two or more waveforms and how each waveform changes on relation the others. A diagram like this can be observed directly on a logic analyzer.

Summary Serial and Parallel Data Data refers to groups of bits, which represented by digital waveforms must be transferred from one circuit to another(from memory to CPU), can be transferred by either serial transfer (sent one bit at a time) or parallel transfer(all bits in a group are sent at the same time).

Summary AND OR NOT Basic Logic Functions True only if all input conditions are true. AND OR True only if one or more input conditions are true. NOT Indicates the opposite condition.

Summary Basic System Functions And, or, and not elements can be combined to form various logic functions. A few examples are: The comparison function Basic arithmetic functions

Summary Basic System Functions The encoding function Convert information such as decimal digit to binary code The decoding function Convert coded information such as Binary number to decimal form

Summary Basic System Functions The data selection function Multiplexer Switches digital data from several input lines onto a single output line Demultiplexer Switches digital data from one input line to several output lines

Summary Basic System Functions The counting function Counter Parallel output lines Binary code for 1 Binary code for 2 Binary code for 3 Binary code for 4 Binary code for 5 1 2 3 4 5 Input pulses Sequence of binary codes that represent the number of input pulses counted. …and other functions such as code conversion and storage.

Summary Integrated Circuits All the logic elements and functions that have been discussed are generally available in integrated circuit (IC) form. integrated circuit (IC) : Is an electronic circuit that is constructed entirely on a single small chip of silicon Fixed-function logic and Programmable logic are two broad categories of digital ICs

Summary Fixed-function logic Fixed-function logic A category of digital integrated circuits having functions that cannot be altered. The logic functions are set by the manufacturer and cannot be altered

Summary Programmable Logic Programmable logic devices (PLDs) are an alternative to fixed function devices. The logic can be programmed for a specific purpose. In general, they cost less and use less board space that fixed function devices.