数字电子技术pp5.ppt

逻辑电路,,组合逻辑电路,时序逻辑电路,功能：输出只取决于 当前的输入组成：门电路，不存在记忆元件功能：输出取决于当前的输入和原来的状态组成：组合电路、记忆元件Combinational logic model,Definition of Combinational Logic 组合逻辑的定义,Logic circuits without feedback from output to the input, constructed from a functionally complete gate set,are said to be combinational,Combinational logic circuit,General principles about implementing combinational logic circuit (chapter 5),Many types of practical and different integrated chips (chapter 6),,5-1 Basic Combinational Logic Circuits (Analysis) 5-2 Implementing（ Design ） Combinational Logic  组合逻辑电路的实现(设计）5-3 The Universal Property of NAND and NOR Gates 5-4 Combinational Logic Using NAND and NOR Gates5-5 Logic Circuit Operation With Pulse Waveform,5 Analysis and Design of Combinational Logic,组合逻辑电路分析和设计,,,,,5-1 Basic Combinational Logic Circuits (Analysis),AND-OR Logic（与-或逻辑电路）AND-OR-Invert Logic（与-或-非逻辑电路）Exclusive-OR Logic（异-或逻辑电路）,AND-OR Logic,Truth table for AND-OR logic in Figure 5-1,AB,CD,X=AB+CD,,SOP,For a 4-input AND-OR logic circuit,the output of X is high if both A and B are high or both C and D are high.,AND-OR Invert Logic,Exclusive-OR Logic: XOR gate is actually combination of other gates.,,Steps:,b. 用逻辑代数或卡诺图对逻辑代数进行化简。

c. 列出输入输出真值表并得出结论电路 结构,,输入输出之间的逻辑关系,a. 由给定的逻辑图逐级写出逻辑关系表达式Combinational logic analysis,1,Example: analyze the following circuit, then figure out its function.,0,1,Be locked!,1,B,1,0,Be locked!,1,Trait: select channel A while M=1； select channel B while M=05-2 Implementing Combinational Logic,From Boolean expression to logic circuitFrom truth table to logic circuit,组合逻辑电路的实现,From Boolean expression to logic circuit - Given a Boolean expression, create a logic circuit that implements that expression.,Logic circuit for X = AB + CDE.,From truth table to logic circuit - Given a truth table, create a logic circuit that implements that table.,注意：同一种逻辑关系可以由不同的电路构成，但同一个逻辑电路只能表达一个逻辑命题。

不同的电路可能实现同一个逻辑关系Tip:,Complement content:,任务要求,,最简单的逻辑电路,设计步骤：,Combinational logic design,Ex 1：设计三人表决电路（A、B、C）每人一个按键，如果同意则按下，不同意则不按结果用指示灯表示，多数同意时指示灯亮，否则不亮a. 首先指明逻辑符号取“0”、“1”的含义b. 根据题意列出真值表真值表,三个按键A、B、C按下时为“1”，不按时为“0”输出是F，多数赞成时是“1”，否则是“0”真值表,c. 画出卡诺图，并用卡诺图化简：,a. 根据逻辑表达式画出逻辑图a) 若用与、或门实现,Ex 2: The monitoring circuit of traffic lights,Input : light on, 1 ; light off, 0Output is “low”: operating correctlyOutput is “high”: operation fails,Logic diagram by using basic gates:,5-3 The Universal Property of NAND and NOR Gates,NAND and NOR gates are “universal” because they can be used to produce any of the other logic functions.,The NAND Gate as a Universal Logic ElementThe NOR Gate as a Universal Logic Element,NAND Gate as an Inverter,The NAND Gate as a Universal Logic Element,Be made from a NAND gate by connecting all of the inputs together.,?,?,Two NAND Gates as an AND Gate,,Three NAND Gates as an OR Gate,Four NAND Gates as NOR Gate,Up to this point, you should understand: basic logic functions (NOT,AND,OR,NOR) can be generated by the use of NAND gates alone.,NOR Gate as an Inverter,The NOR Gate as a Universal Logic Element,Two NOR Gates as an OR Gate,Three NOR Gates as an AND Gate,Four NOR Gates as an NAND Gate,Ex 1: 若用与非门实现,Ex 2: implementing by using NAND gates,Assignment: Quiz of EE3314,A commercial airliner has three parallel flight control computers(A,B and C)to provide safe and reliable navigation and flight stability.All three computers perform the same calculations.The airplane must land immediately if more than one computer fails.Each flight control computer is designed to provide a 1(TRUE) when it is operating correctly.The pilot wants a circuit that shows what he should do.The output F should be 1(TRUE) when two or more computers have failed.sketch the circuit using a minimum number of logic gates.a)Construct the truth tableb)Minimize the logic functionc)Sketch the circuit(using NAND gates),5-4 COMBINATIONAL LOGIC USING NAND AND NOR GATES,NAND LOGICNOR LOGIC,NAND LOGIC A NAND gate can function as either a NAND or a negative-OR gate.,,,NAND,negative-OR,NAND logic for X = AB + CD.,Development of the AND-OR equivalent.,Illustration of the use of the appropriate dual symbols in a NAND logic diagram.,,NOR LOGIC A NOR gate could function as either a NOR or a negative-AND.,,,NOR,negative-AND,NOR logic for X = (A + B)(C + D),5-5 CIRCUIT OPERATION WITH PULSE WAVEFORM INPUTS,Keep in mind that the operation of each gate is the same for pulse waveform inputs as for constant-level inputs.The output of a logic circuit at any given time depends on the inputs at that particular time.,Determine the final output waveform X for the circuit with input waveforms A,B ,and C as shown.,。