EDA技术P2-PLD结构原理

1EDA技术PLD基本结构原理2可编程逻辑器件基本结构原理在上一部分我们提到可编程逻辑器件（ProgrammableLogicDevices，PLD），它是大规模集成电路的产物，是一种半定制的集成电路(可编程），结合EDA技术可快速、方便地构建数字系统。本部分将具体讨论PLD的结构和工作原理。◆基础部分为教材的CHAPER6；（掌握关键词和基本编程原理）◆扩展对CPLD的乘积项原理和FPGA的查找表原理进行剖析；◆最后介绍相关的编程下载测试技术及常用的主流FPGA和CPLD产品。32.1Programmablelogicdevices1.InternalstructureofPLDsPLD内部结构PLDscontaingatesandflip-flopssothattheinterconnectionbetweenthecomponentscanbealteredtoimplementvariouslogicfunctions.PLD包含门和触发器，改变元件间互连关系得以实现各种逻辑功能。●CombinationallogicPLDsthatcontainingonlybasiclogicgatesareusuallyorganizedasanarrayofANDgatesandORgatesthatimplementsum-of-productexpressions.●组合逻辑PLD只包含基本的逻辑门，一般配置为与、或门阵列实现的积之和表达式。●SequentiallogicPLDsaddflip-flopstotheoutputs.●时序逻辑PLD，在输出增加了触发器。42.1Programmablelogicdevices无论是何种逻辑形式，PLD都要求通过改变内部互联关系，形成不同的逻辑配置。Whateverlogicarrangement,ageneralrequirementofaPLDistohaveameansofchangingtheinterconnectionstoformadifferentlogicconfigurationThePrincipleStructureofaSimplePLDForExample52.1Programmablelogicdevices2.DevelopmentofPLDsPLD的发展Theoriginalmethodwastomanufacturethedeviceswithsemiconductorfuses.Initiallytheyareintactwithinthedevicewhichprovidesextensiveinterconnections.Selectedfusesarethen“blown”bytheusertoobtainthedesiredinterconnectionsusingspecialPLDprogrammer.最早制备PLD的方法是采用半导体熔丝。出厂时器件内所有熔丝是连通的，可提供多种互联关系。使用专用的PLD编程器，由用户选择“烧断”哪些熔丝，获得所需的互联关系。Onceafuseisblown,theconnectioncannotberemade.Therefore,theyarenotre-programmable.熔丝一旦烧断，不可恢复。因此，他们是不可重编程的。62.1Programmablelogicdevices现在，可编程PLD采用的是半导体可擦除只读存储器技术。Now,programmablePLDsareavailablewhichusesemiconductorerasableread-onlymemorytechnology.Theconnectionsdependuponstoredbinaryinformation.Amemorycellexistsateachconnectionpointtostorea0tomaintainaconnectionora1todisableaconnection.（连接点）是否连接取决于存储的二进制信息。（阵列的)每个交叉点都制作存储元件，0表示保持连接,1表示断开。Semiconductormemory-basedPLDsprovidethecapabilitytoaltertheinterconnectionsrapidlyandmanytimes.基于半导存储器的PLD可快速、多次修改内部连接。72.1Programmablelogicdevices制造商还生产固定连接的PLD。要实现固定连接，必须创建专用集成电路的掩膜（文件）。ManufacturersalsoproducePLDswithpermanentconnections.Toachievethefixedconnections,specificintegratedcircuitmasksmustbecreated.Summaryone-timeprogrammabletype(一次性可编程型)usingsemiconductorfuses(采用半导体熔丝技术）beusedforasmallproductionrun(用于小批量生产）Re-programmabletype（可重复编程型）memorytechnology（采用存储技术）beusedforexperimention（用于研发）manufacturedPLDstype（掩模型）Manufacturerconnections（掩模连接技术）beusedforalargeprodutionrun(用于大批量生产）ThreetypeofPLDs82.2CombinationalcircuitPLDs（组合电路PLD）1.ProgrammablelogicarraysPLAsTheinterconnectionstructureforacombinationalcircuitPLDisatwo-dimensionalarraywithprogrammableconnectionsatthecrossoverpoints.可编程逻辑阵列---PLA组合电路PLD是由交叉点可编程连接的两维阵列构成。92.2CombinationalcircuitPLDsSimplifiedfieldprogrammablelogicarraydiagram简单现场可编程逻辑阵列示意图APLAwith16inputsand8independentoutputs一个16输入8独立输出的PLA32输入，乘积项48输入和项积之和102.2CombinationalcircuitPLDsEachoutputcanproduceasum-of-productexpressionconsistingofupto48productterms,andeachproducttermcanhaveupto16inputvariablesortheirinverse.ThenumberofproducttermsisdeterminedbythenumberofANDgates,andthenumberofvariablesineachproducttermisdeterminedbythenumberofinputstothecircuit.Thecrossoverconnectionsaredonewithasemiconductorfuseinserieswithadiodetoformtheinputofagate.每路输出为最多48个乘积项之和组成，每个乘积项有最多16个输入量或其反相输入。乘积项数量决定于与门的数量，每个乘积项输入量，决定于（集成）电路的输入引脚数量。半导体熔丝与二极管串联，实现交叉点连接，构成逻辑门输入112.2CombinationalcircuitPLDsTherearefourconditionsforeachinputvariables.(a)Un-programmedstate:Boththetrueandinversevariablesconnectionsareleftintact.(b)Truevariableselected:Thetruevariableisselectedbyremovingtheinverseconnection.(c)Inversevariableselected:Theinversevariableisselectedbyremovingthetrueconnection.(d)Novariableselected:Bothconnectionsareremoved.(a)未编程状态原变量和反变量均被完整保留(连接)(b)选择原变量断掉反变量连接，来选择原变量(c)选择反变量断掉原变量连接，来选择反变量(d)未选择变量断掉所有变量每个输入变量有四种接入情况(a)(b)(c)(d)122.2CombinationalcircuitPLDsExp1:UsingaPLAtogeneratethefunctionf1=ABCf2=AB+BCTheX’sindicatetheconnectionsareleftintact.APLAisbestusedwhenseveralsum-of-productexpressionsarerequired,especiallyifthesum-of-produtexpressionshavemanymoretermsthanaregiveninthisexample.例1:用PLA实现以下功能f1=ABCf2=AB+BCX表示完全连接当需要实现多个积之和时，特别是式中含有比上例更多的乘积项时，使用PLA最合适。上图有误！！！132.2CombinationalcircuitPLDsExp2:ToimplementthefunctionIfafunctiontobeimplementedisnotinsum-of-productform,itneedstobeconvertedintothisform.PLDsoftwareisavailablewhichwillconvertBooleanexpressionsintotheappropriateform.如要实现的功能不是积之和形式，则需要转换成积之和形式。例2：实现如下功能PLD软件就是用于将布尔表达式转换为适合的表达形式。)(BACfExpandintosum-of-productform:))()(BCACBABABACBACf展开转化成积之和形式：142.2CombinationalcircuitPLDs2.ProgrammablearraylogicPALPALhasonlyprogrammableconnectionstotheinputsoftheANDgates.InaPAL,eachANDgateisdirectlywiredtooneinputofoneORgate.Afixednumberofproductterms,greatlysimplifyingdesignandimprovingoperationspeedThePLAhasbothprogrammableconnectionstotheinputstoANDgatesandORgates.Programmableconnectionsincuragreaterdelaythandirectwiredconnections.PLA采用了可编程的与阵列和可编程或阵列，而可编程连接要比直接固定连接产生的迟延时间长得多。PAL只用可编程与门阵列，每个与阵列固定与或阵列连接。可编程阵列逻辑--PAL乘积项数目固定，大大简化设计，提高运算速度1516--Maximumof16variablesPAL16L8isanexampleofacombinationalcircuitPAL.L—Theoutputsareinverted(