《电子技术数字基础 Digital Fundamentals》双语课件PPT-第03章 Logic Gates

1、13 Logic Gates2Contentsw Basic Logic Operationsw The Inverterw The AND Gatew The OR Gatew The NAND Gatew The NOR Gatew The Exclusive-OR Gatew The Exclusive-NOR Gate31-3 Basic Logic Operations（基本逻辑运算）NOT Logic Operation （非运算）（非运算）AND Logic Operation （与运算）（与运算）OR Logic Operation （或运算）（或运算）41-3-1 NOT L

2、ogic Operationw The NOT operation changes one logic level to the opposite logic level. If the input is HIGH(1), the output is LOW (0), and vice versa.51-3-1 NOT Logic Operationw Function （逻辑功能）（逻辑功能）: changes one logic level to the opposite level. Changes a 1 to a 0 and a 0 to a 1.EYALogic symbol61-

3、3 Basic Logic Operationsw Logic symbol （逻辑符号） : some standard distinctive shape symbol.7w Logic gate (逻辑门）逻辑门）: the circuit that performs a specified logic operationw Inputs, outputs （输入，输出）（输入，输出）: the lines connected to each symbol (gate). AND and OR gates can have any number of inputs; NOT gate h

4、as only one input.1-3 Basic Logic Operations8The gate to perform the NOT logic operation is called an inverter （反相器（反相器,非门）非门）.1-3-1 The Inverter93-1 The Inverterw Truth table（真值表）： shows the output for each possible input in terms of levels and corresponding bits. Inverter Truth Table103-1 The Inve

5、rterw Inverter operation (反相器运算）w For a pulse input, when the input is LOW(0), the output is HIGH(1); when the input is HIGH, the output is LOW, thereby producing an inverted output pulse.113-1 The Inverterw Timing Diagrams （时序图） is basically a graph that accurately displays the relationship of two

6、or more waveforms with respect to each other on a time basis.123-1 The Inverter w ex. A waveform is applied to an inverter in the following figure, show the timing diagram.133-1 The Inverter Logic Expression (逻辑表达式)w In Boolean algebra(布尔代数）, which is the mathematics of logic circuits and will be co

7、vered in Chapter 4, a variable ( a symbol used to represent a logical quantity) is designated by a letter.w The complement of a variable (反变量）is designated by a bar over the letter. w A variable can take on a value of either 1 or 0.A143-1 The Inverter Logic ExpressionLogic expression（逻辑表达式） for the

8、inverterw If the variable is called A and the output variable is called X (中文课本多用F表示),thenw The complement variable can be read as “A bar” or “not A” （A反）.w If A=0, =1AX A151-3-2 AND Logic Operation（与逻辑操作）EABYThe AND operation produces a HIGH output only if all the inputs are HIGH.When any of the in

9、puts is LOW, the output is LOW.163-2 The AND Gate （与门）w The operation is implemented by an AND gate.w The basic purpose of an AND gate is to determine when certain conditions are simultaneously true.A possible logic levels for a 2-input(2输入） AND gate173-2 The AND Gate Truth TableThe truth table for

10、a 2-input AND gate183-2 The AND Gate Timing Diagram193-2 The AND Gate Logic Expressionw For a 2-input AND gate, if one input variable is A, the other one is B, and the output variable is X, then the Boolean expression is X=AB or X=ABw The AND function is the same as Boolean multiplication. 00=0, 01=

11、0, 10=0, 11=1201-3-3 OR Logic Operation（或逻辑操作）w The OR operation produces a HIGH output when any of the inputs is HIGH.w The output is LOW only when all of the inputs are LOW.AEBY 213-3 The OR Gate （或门）w The OR operation is implemented by a OR gate. A possible logic levels for a 2-input OR gate223-3

12、 The OR Gate Truth Table The truth table for a 2-input OR gate233-3 The OR Gate Timing Diagram243-3 The OR Gate Logic Expressionw For a 2-input ORgate, if one input variable is A, the other one is B, and the output variable is X, then the Boolean expression is X=A+Bw The OR function is the same as B

13、oolean addittion. 0+0=0, 0+1=1, 1+0=1, 1+1=1253-4 The NAND Gate (与非门）w The term NAND is a contraction （缩写） of NOT-AND and implies an AND function with a complemented (inverted) output. 263-4 The NAND Gatew The NAND gate produces a LOW output only when all the inputs are HIGH.w For a 2-input NAND gat

14、e, the output X is HIGH if either A or B is LOW, and HIGH if both A and B are LOW.273-4 The NAND Gate Truth TableThe truth table for a 2-input NAND gate283-4 The NAND Gate Logic Expression The Boolean expression for the output of a 2-input NAND gate is NAND gates can be used in combination to perfor

15、m the AND，OR and inverter operation.ABX 293-5 The NOR Gate （或非门）w The term NOR is a contraction of NOT-OR and implies an OR function with a complemented (inverted) output. 303-5 The NOR Gatew The NOR gate produces a LOW output when any of the inputs is HIGH, and HIGH only when all of its input are L

16、OW.w For a 2-input NOR gate, the output X is LOW if either A or B is HIGH, and HIGH if both A and B are LOW.313-5 The NOR Gate Truth TableThe truth table for a 2-input NOR gate323-5 The NOR Gate Logic Expressionw The Boolean expression for the output of a 2-input NOR gate isw NOR gates can be also u

17、sed in combination to perform the AND，OR and inverter operation.BAX333-6 The Exclusive-OR Gate (XOR) （异或门）w The output of an exclusive-OR gate is HIGH only when the two inputs are at opposite logic levels.343-6 The Exclusive-OR Gate For an exclusive-OR gate, output X is HIGH if input A is LOW and in

18、put B is HIGH, or if A is HIGH and B is LOW; X is LOW if A and B are both HIGH or both LOW.353-6 The Exclusive-OR Gate Truth TableTruth table for an exclusive-OR gateLogic ExpressionBABABAX363-7 The Exclusive-NOR Gate (XNOR) （同或门）w The output of an exclusive-NOR gate is HIGH only when the two inputs are at the same logic levels.373-7 The Exclusive-NOR Gatew For an