解析編碼器的三態(tài)門

解析編碼器的三態(tài)門低位Yi=EN·miG1G2A_LG2B_LENYi_L=Yi’=(EN·mi)’EN=G1·G2A·G2B=G1·G2A_L’·G2B_L’Y0_LY1_LY7_LY2_LY3_LY4_LY5_LY6_LEN解析編碼器的三態(tài)門ZYXABCG1G2AG2BY0Y1Y2Y3Y4Y5Y6Y774x138+5VFAnswerkeyforexercise1解析編碼器的三態(tài)門Answerkeyforexercise2解析編碼器的三態(tài)門Example1解析編碼器的三態(tài)門Answerkeyforexample1解析編碼器的三態(tài)門ReviewofLastClass

Decoder74X13874X139CascadingBinaryDecodersBCDDecoderSeven-SegmentDecoders解析編碼器的三態(tài)門G1G2A-LG2B-LBCAY0_LY1_LY7_LY2_LY3_LY4_LY5_LY6_L低位高位Yi=EN·miYi_L=Yi’=(EN·mi)’The74x1383-to-8Decoder解析編碼器的三態(tài)門74x139

The74x139Dual2-to-4Decoder解析編碼器的三態(tài)門N0N1N2N3EN_L+5VD0_LD7_LD8_LD15_L思路：

16個(gè)輸出需要

2片74x138？Y0Y7ABCG1G2AG2BY0Y7ABCG1G2AG2BU1U2任何時(shí)刻只有一片在工作。

4個(gè)輸入中，N3位控制片選N2N1N0位控制輸入designthe4-to-16decoder解析編碼器的三態(tài)門二-十進(jìn)制譯碼器00000001001000110100010101100111100010011010101111001101111011110111111111101111111111011111111110111111111101111111111011111111110111111111101111111111011111111110111111111111111111111111111111111111111111111111111111111111I3

I2

I1

I00123456789Y0_L

Y9_L偽碼任意項(xiàng)BCDDecoder解析編碼器的三態(tài)門Seven-SegmentDecodersabcdefgdp公共陰極abcdefgdpNormallyuse(常用的有)：Light-EmittingDiodes（LED,半導(dǎo)體數(shù)碼管）Liquid-CrystalDisplay（LCD,液晶數(shù)碼管）abcdefgdp公共陽(yáng)極解析編碼器的三態(tài)門七段顯示譯碼器的真值表00000001001000110100010101100111100010011010101111001101111011111111110011000011011011111001011001110110110011111111000011111111110011000110100110010100011100101100011110000000A3

A2

A1

A0abcdefg0123456789101112131415解析編碼器的三態(tài)門6.5Encoder解析編碼器的三態(tài)門

ENCODER

(P408)Ifthedevice’soutputcodehasfewerbitsthantheinputcode,thedeviceisusuallycalledanencoder.Probablythesimplestencodertobuildisa2n-to-norbinaryencoder.解析編碼器的三態(tài)門encoder（編碼器）Binaryencoder

Y0Y1Y2I0I1I71000000000001000000001001000000100001000001100001000100000001001010000001011000000001111I0I1I2I3I4I5I6I7Y2Y1Y0Thetruthtablefora8-to-3binarydecoder2ninputsnoutputs解析編碼器的三態(tài)門encoder（編碼器）Y0=I1+I3+I5+I7Y1=I2+I3+I6+I7Y2=I4+I5+I6+I7前提：任何時(shí)刻只有一個(gè)輸入端有效。1000000000001000000001001000000100001000001100001000100000001001010000001011000000001111I0I1I2I3I4I5I6I7Y2Y1Y0Thetruthtablefora8-to-3binarydecoder解析編碼器的三態(tài)門Binaryencoder

Y0Y1Y2I0I1I72ninputsnoutputs解析編碼器的三態(tài)門encoder（編碼器）Y0=I1+I3+I5+I7Y1=I2+I3+I6+I7Y2=I4+I5+I6+I7前提：任何時(shí)刻只有一個(gè)輸入端有效。Trouble:WhenmorethanOneInputsareasserted?優(yōu)先級(jí)（priority）1000000000001000000001001000000100001000001100001000100000001001010000001011000000001111I0I1I2I3I4I5I6I7Y2Y1Y0Thetruthtablefora8-to-3binarydecoder解析編碼器的三態(tài)門Ifmultiplerequestscanbemadesimultaneously,howcantheencodingdevicedecidewhich?Thesolutionistoassignprioritytotheinputlines,sothatwhenmultiplerequestsareasserted,theencodingdeviceproducesthenumberofthehighest-priorityrequestor.Suchadeviceiscalledapriorityencoder.(P408)解析編碼器的三態(tài)門6.5.1PriorityEncoders(P410)(優(yōu)先編碼器)A2A1A0IDLEI7I6I5I4I3I2I1I0將I0～I(xiàn)7轉(zhuǎn)換為H0～H7，保證其中，任何時(shí)刻只有一個(gè)有效H7=I7H6=I6·I7’H5=I5·I6’·I7’…H0=I0·I1’·I2’·…·I6’·I7’A2=H4+H5+H6+H7A1=H2+H3+H6+H7A0=H1+H3+H5+H7Highest-Priority數(shù)大優(yōu)先

如果沒有輸入有效，則IDLE為1IDLE=I1’·I2’·…·I6’·I7’解析編碼器的三態(tài)門Logicsymbolforageneric8-inputpriorityencoder.解析編碼器的三態(tài)門6.5.2The74x148PriorityEncoder

(P411)The74x148isacommerciallyavailable,MSI8-inputpriorityencoder.解析編碼器的三態(tài)門EI-LI7-LI6-LI5-LI4-LI3-LI2-LI1-LI0-LA2-LA1-LA0-LGS-LEO-Litsinputsandoutputsareactivelow.

解析編碼器的三態(tài)門inputsoutputsEnableoutput使能輸出，用于級(jí)聯(lián)EOGroupSelect(選通輸出)GSEI_L有效沒有輸入請(qǐng)求EO_L有效EnableInputs使能輸入EI-LEI_L有效有輸入請(qǐng)求GS_L有效P411解析編碼器的三態(tài)門解析編碼器的三態(tài)門TheEO_Lsignalisanenableoutputdesignedtobeconnectedto

theEI_Linputofanother’148thathandleslower-priorityrequests.(P412)解析編碼器的三態(tài)門lower-priority’148Higher-priority’148解析編碼器的三態(tài)門Two74x148cascadedtohandle16requests.Q15_LQ8_LQ7_LQ0_LY3Y2Y1Y0GSQ15-L......QO-LY3Y2Y1Y00XX……..X11111………….00000解析編碼器的三態(tài)門A2A1A0GSEOEII7I0A2A1A0GSEOEII7I0Q15_LQ8_LQ7_LQ0_LY0Y1Y2Y3GSTwo74x148cascadedtohandle16requests.級(jí)聯(lián)為16－4優(yōu)先編碼器解析編碼器的三態(tài)門輸入：由864，需8片74x148每片優(yōu)先級(jí)不同（怎樣實(shí)現(xiàn)？）保證高位無輸入請(qǐng)求時(shí)，次高位才工作高位芯片的EO-L端接次高位芯片的EI-L端用8-3優(yōu)先編碼器74x148級(jí)聯(lián)為64-6優(yōu)先編碼器A2A1A0GSEOEII7I0片間優(yōu)先級(jí)的編碼

——

利用第9片74x148

每片的GS端接到第9片的輸入端

第9片的輸出作為高3位（RA5～RA3）片內(nèi)優(yōu)先級(jí)片間優(yōu)先級(jí)

輸出：6位低3位高3位8片輸出A2～A0通過或門作為最終輸出的低3位RA2～RA0(P413)解析編碼器的三態(tài)門解析編碼器的三態(tài)門分析判定優(yōu)先級(jí)電路：（利用74x148）

8個(gè)___電平有效輸入I0_L～I(xiàn)7_L，_____的優(yōu)先級(jí)最高地址輸出A2～A0，____電平有效若輸出AVALID高電平有效，則表示_______________A2A1A0GSEOEI74x148I7I0I0_LI7_LA2A1A0AVALID低I0_L至少有一個(gè)輸入有效高解析編碼器的三態(tài)門設(shè)計(jì)判定優(yōu)先級(jí)電路：（利用74x148）

8個(gè)輸入I0～I(xiàn)7高電平有效，I7優(yōu)先級(jí)最高地址輸出A2～A0，高電平有效如果沒有輸入有效，A2～A0為000且輸出IDLE=1有效I7I0A2A1A0IDLEA2A1A0GSEOEII7I074x148解析編碼器的三態(tài)門Examplefor74XX148利用優(yōu)先編碼器（PriorityEncoder）74x148構(gòu)成8421BCD碼編碼器(BCDEncoder)?！窘獯稹?/p>

當(dāng)輸入為D8_L或D9_L時(shí)，需要另外添加電路實(shí)現(xiàn)編碼，由于D8_L的BCD編碼為0111，D9_L的BCD編碼為0110，而D0_L~D7_L的編碼最高位(MSB)都為1，因此BCD碼編碼器的最高位(MSB)輸出為。當(dāng)74x148優(yōu)先編碼器的編碼使能端(EncoderEnable)EI_L=1時(shí)，編碼器不工作，編碼輸出端Y2_L、Y1_L和Y0_L都為1，因此令，，用優(yōu)先編碼器74x148和門電路，可以構(gòu)成BCD碼編碼器，如圖所示。解析編碼器的三態(tài)門解析編碼器的三態(tài)門6.6Three-StateDevices

(三態(tài)緩沖器)解析編碼器的三態(tài)門6.6Three-StateDevices

(三態(tài)緩沖器)(P418)Themostbasicthree-statedeviceisathree-statebuffer,oftencalledathree-statedriver.Theextrasignalatthetopofthesymbolisathree-stateenableinput,whichmaybeactivehighoractivelow,Whentheenableinputisasserted,thedevicebehaveslikeanordinarybufferorinverter.Whentheenableinputisnegated,thedeviceoutput“floats”;thatis,itgoestoahighimpedance(Hi-Z),disconnectedstateandfunctionallybehavesasifitweren’teventhere.解析編碼器的三態(tài)門6.6Three-StateDevices

(三態(tài)緩沖器)(P418)三態(tài)緩沖器（三態(tài)驅(qū)動(dòng)器）74x125：低電平使能，輸出不反相74x126：高電平使能，輸出不反相獨(dú)立使能74x541：兩個(gè)公共使能端，低電平使能，施密特觸發(fā)輸入，輸出不反相（P272圖5-57）

標(biāo)準(zhǔn)SSI和MSI三態(tài)緩沖器解析編碼器的三態(tài)門Typicalthree-statedevicesaredesignedsothattheygointotheHi-Zstatefaster