3.1 DIGITAL ELECTRONICS 53 Most logic gates have two inputs and one output. The input and the output signals of a gate can be in one of the two binary conditions: low (0) or high (1). The value of the output depends on the values of its inputs. The truth table gives a list of all the possible combinations of inputs and the resulting output. ONLINE RESOURCES Algorithms and flowcharts The binary system and the units of measure AND IN OUT 0 0 1 1 0 1 0 1 0 0 0 1 IN IN OUT 0 0 1 1 0 1 0 1 0 1 1 1 and OR OUT 0 1 1 0 120 MECHATRONICS MechPower.indb 120 Key differences Analogue signal Digital signal It is a continuous signal. It uses a continuous range of values. It is represented by a sine-wave. It varies constantly from instant to instant. The bandwidth of the analogue signal is low. It is suited for audio and video transmission. It is a time-separated signal. It uses the discrete values 0 and 1. It is represented by a square wave. It exists only at one of a set of levels. The bandwidth of the digital signal is high. It is suited to computing and digital electronics. Logic gates Most electronic devices perform operations by passing data through a number of logic gates which operate as electronic switches that react in one of the two ways of the binary code to the data put into it. There are three basic logic gates: AND, OR, NOT. The simplest possible gate is called an inverter, or a NOT gate. It has an input, and the output is its opposite: if the input is 1, the output is 0 and vice versa. An AND gate is a circuit with two inputs and an output which is set to 1 only if both the inputs are 1. An OR gate is set to 1 if at least one input is one and 0 if both the inputs are 0. Other logic gates are: NAND, NOR, XOR and XNOR, which are combinations of the previous logic gates. NAND or IN 0 0 1 1 NOT IN Signals Analogue and digital signals are used to transmit information such as audio or video into electric signals. In analogue technology, information is translated into electric pulses of varying amplitude. In digital technology, translation of information is into binary format (zero or one), where each bit is representative of two distinct amplitudes. Digital circuits are preferred because of the ease with which their output can be manipulated by computers and because digital signals are less subject to transmission errors, more immune to noise and because they can be stored and manipulated without degradation. Computers and digital signals As computers are made up of digital electronics, internally they respond to two kinds of electrical states: on or off : these two conditions are represented by the two numbers: 0 and 1. The on position corresponds to a 1, and the off position to a 0. Therefore, computers use binary numbers, called binary digits or bits (short for binary digit) in place of decimal digits. discrete: separato ease: facilità set: serie sine-wave: onda sinusoidale switch: interruttore IN ANALOGUE vs DIGITAL not NOR IN OUT 0 1 0 1 1 1 1 0 nand EXCLUSIVE OR IN IN OUT 0 0 1 1 0 1 0 1 1 0 0 0 nor EXCLUSIVE NOR IN IN OUT 0 0 1 1 0 1 0 1 0 1 1 0 xor IN IN OUT 0 0 1 1 0 1 0 1 1 0 0 1 xnor 30/01/24 17:08