自动化专业英语unit 3 A.ppt

Translation A very common method of digital operation is achieved by using voltage pulses．The presence of a positive pulse can be represented by 1 and the absence of a pulse by 0．With a square-wave signal，the positive pulses can represent 1 and the negative pulses can represent 0． Translation Integrated circuits containing many transistors are most commonly used as switching devices in digital electronics logic gates．The three basic types of digital logic gates are the AND gate，the OR gate，and the NOT gate (as shown in Fig．3-1)．The operation of an AND gate is mathematically expressed by the equation A×B = C．This can be read as “input A and input B equals output C”．The operation of an OR gate is often expressed by the equation A+B = C．This can be read as “either input A or input B (or both) equals output C”．An important function of NOT gate is to produce signal inversion or an output signal that is opposite in nature to the input signal．Any logic function can be performed by the three basic gates that have been described．Even in a large scale digital system，such as a computer，control，or digital-communication system，there are only a few basic operations，which must be performed．The three basic types of digital logic gates and the flip-flop are the four circuits most commonly employed in such systems． Translation A B C A×B=C ≥1 A B C A+B=C 1 A C ○ A = C Fig．3-1 Digital Logic Gates New words and phrases primarily [praim?r?li] adv. 主要地，根本上；首先；最初的 binary [bain?ri] adj. 二元的，二态的；二进制的 pulse [p?ls] n. 脉搏；脉冲vt. 使跳动vi. 跳动，脉跳 represent [reprizent] vt. vi. 表现；描绘；代表；回忆；再赠送 nature [neit??] n. 自然；性质；种类；本性 inversion [inv?:??n] n. 倒置；倒转；反向反转 New words and phrases scale [skeil] n.刻度，衡量，数值范围 v. 依比例决定；攀登 flip-flop [flipfl?p] n. 触发器；啪嗒啪嗒的响声vt. 使翻转；使突然转变 the closed-switch state 开关闭合状态 the open-switch state 开关断开状态 logic gates [计算机] 逻辑闸；逻辑门电路库；逻辑门 and gate 和门；与门；与电路 binary arithmetic 二进制算术 Exercises I．Write T (True) or F (False) after the following statements according to the text. 1．