原文-标准并口程序

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1、InterfacingtheStandardParallelPortTableofContents•IntroductiontoParallelPorts•HardwareProperties•Centronics?•PortAddresses•SoftwareRegisters-StandardParallelPort(SPP)•UsingTheParallelPorttoInput8Bits.•ParallelPortModesinBIOS•ParallelPortModesandtheECP'sExtendedControlRe

2、gisterIntroductiontoParallelPortsTheParallelPortisthemostcommonlyusedportforinterfacinghomemadeprojects.Thisportwillallowtheinputofupto9bitsortheoutputof12bitsatanyonegiventime,thusrequiringminimalexternalcircuitrytoimplementmanysimplertasks.Theportiscomposedof4controll

3、ines,5statuslinesand8datalines.It'sfoundcommonlyonthebackofyourPCasaD-Type25Pinfemaleconnector.TheremayalsobeaD-Type25pinmaleconnector.NewerParallelPortasarestandardizedundertheIEEE1284standardfirstreleasedin1994.Thisstandarddefines5modesofoperationwhichareasfollows,1.C

4、ompatibilityMode.2.NibbleMode.(ProtocolnotDescribedinthisDocument)3.ByteMode.(ProtocolnotDescribedinthisDocument)4.EPPMode(EnhancedParallelPort).5.ECPMode(ExtendedCapabilitiesPort).Theaimwastodesignnewdriversanddeviceswhichwerecompatiblewitheachotherandalsobackwardscomp

5、atiblewiththeStandardParallelPort(SPP).Compatibility,Nibble&BytemodesusejustthestandardhardwareavailableontheoriginalParallelPortcardswhileEPP&ECPmodesrequireadditionalhardwarewhichcanrunatfasterspeeds,whilestillbeingdownwardscompatiblewiththeStandardParallelPort.Compat

6、ibilitymodeornCentronicsMode1*asitiscommonlyknown,canonlysenddataintheforwarddirectionatatypicalspeedof50kbytespersecondbutcanbeashighas150+kbytesasecond.Inordertoreceivedata,youmustchangethemodetoeitherNibbleorBytemode.Nibblemodecaninputanibble(4bits)inthereversedirect

7、ion.E.g.fromdevicetocomputer.BytemodeusestheParallefsbi-directionalfeature(foundonlyonsomecards)toinputabyte(8bits)ofdatainthereversedirection.ExtendedandEnhancedParallelPortsuseadditionalhardwaretogenerateandmanagehandshaking.Tooutputabytetoaprinter(oranythinginthatmat

8、ter)usingcompatibilitymode,thesoftwaremust.1.WritethebytetotheDataPort.2.Checktoseeistheprinterisbusy.Ifthepri