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1、CH3 LOGIC GATES1.Logical operation2.2. Application3.3. Troubleshooting of logic gates4.4. WaveformsChapter overview1.The standard logic symbol3-1 The InverterDistinctive shape symbolsRectangular outline symbolsThe negation indicatorsThe polarity indicators2. Truth table Inputs outputs A X 0 1 1 03.
2、Operation4. Timing diagram5. Logic expression:6. Application example: 1s complement circuit1. The standard logic symbolABX3-2 The And GateDistinctive shape XABRectangular outline 3. AND OperationIf inputs A and B are HIGH, output X is HIGH; If either A or B is LOW, or if both A and B are LOW, X is L
3、OW 4. Truth table Inputs outputs A B X 0 0 0 0 1 0 1 0 0 1 1 1Table 3-2 Truth table for a 2-input AND gate3. Pulsed Operation Omission(P105,e.g. 3-3)ABX X=AB Or 4. Logic expressionBoolean multiplication5. Application exampleThe AND Gate as an Enable/Inhibit Device Fig. 3-15 p1081. The standard logic
4、 symbol3-3 The OR Gate1XABRectangular outline XABDistinctive shape symbol2. Logical Operationif either input A or B is HIGH, output X is HIGH if both A and B are HIGH; X is HIGH if both A and B are LOW, X is low .3. Truth table Inputs outputs A B X 0 0 0 0 1 1 1 0 1 1 1 14. Pulsed OperationABX5. Log
5、ic expression X=A+BBoolean addition is the same as the OR function4. Application exampleFig. 3-24Intrusion detection and alarm systemThe NAND is a universal gate ,It can be used in combination to perform the AND, OR, and inverter operations.3-4 The NAND Gate1.The standard logic symbolRectangular out
6、line symbolXABXABDistinctive shape symbol 1.The standard logic symbol2.Logical Operation3.Truth table4.Pulsed Operation5.Logic expression6. (Omisssion)3-5 The NOR Gate3-6 The EXCLUSIVE-OR and EXCLUSIVE-NOR Gates=1XABXABThe standard logic symbol1.CMOS: 2.Complementary Metal-Oxide Semiconductor 3.Wide
7、ly used in VLSI, ULSI 3-7 Integrated circuit logic gatesCMOS and TTL are the most widely used IC technologies, ECL is used in more specialized applications 4000 400074HC 74HCT74VHC 74VHCT速度慢速度慢与与TTL不不兼容兼容抗干扰抗干扰功耗低功耗低74LVC 74AUC速度加快速度加快与与TTL兼容兼容负载能力强负载能力强抗干扰抗干扰功耗低功耗低速度两倍于速度两倍于74HC与与TTL兼容兼容负载能力强负载能力强抗
8、干扰抗干扰功耗低功耗低低低( (超低超低) )电压电压速度更加快速度更加快与与TTL兼容兼容负载能力强负载能力强抗干扰功耗低抗干扰功耗低2. TTL: Transistor-Transistor LogicUsed in MSI, LSI74LS series 74 series74 series74AS series 74ALS series3-7 Performance characteristics and parameters输出输出高电平高电平+VDD VOH(min)VOL(max) 0 G1门门vO范围范围 vO 输出输出低电平低电平 输入输入高电平高电平VIH(min) VIL(max) +VDD 0 G2门门vI范围范围 输入输入低电平低电平 vI vO vI 驱动门驱动门G1 负载门负载门G2 1 1 3-8 Troubleshooting3-9 Digital system application
