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ID:9855293
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时间:2018-05-12
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1、时光荏苒,岁月如白驹过隙,不经意间,我们即将从多彩的大学毕业,完成一个从大学生到社会人的转变。四年的大学生涯,让我明白了许许多多的科学知识和人生哲理,以及数不尽的感悟和成长。然只有将所学的理论知识付诸于社会的实践,才能检验和实现理论自身的价值,也只有将理论付诸于实践才能使理论得以检验。同样,一个人的价值也是通过实践活动来实现的,也只有通过实践才能锻炼人的品质,彰显人的时代风貌。而毕业实习作为大学的最后一课,也是最后一刻,我倍加珍惜,从而可以较深层次的理解社会,以便为将来能更好的胜任工作打下坚实的基础。毕业设计外文资料Da
2、taTransferTechniquesTheactualtransferofdatabetweenthemicrocomputerandexternalandexternaldevicesiscommonlycarriedoutusingthreedifferenttechniques:(1)ling;(2)errupters;(3)emoryaccess;Thesetechniquescanbeusedindividuallyorincombination..PollingPollingroutinesareused
3、forprogrammedinput/outputpurposes.Anumberofperipheraldevicesattachedtothemicrocomouterarecontinuouslypolledatspecifiedtimeintervalstodeterminethedevicewishestoinputdatatothemicroproccssor.Similarly,forthetransferofdatatoanoutputdevice,thestateofitsbufferischecked
4、todetermineifitisemptyandreadytoreceivethedata.Asoftprogramisrequiredtocheckthestateoftheperipheraldevices.Hardwareflagaareusedtoindacatethesendorreceiveconditionoftheperipheral.Ifadeviceisreadytotransferthedata,thenanappropriatesoftwareroutineisusedtoservicethat
5、particulardevicesothatdatatransfercantakeplace.Itisnecessarytoensurethatnoneofthedatafromanyoftheperipheralsarelostwhilethepollingroutinesoranytheperipheraldevicesservicingroutinesarebeingexecuted.Theprobabilityofloseingdataisverysmallsincemostperpheralareslowdei
6、ces.Othertechniques,suchasdirectmemoryaccess(DMA),canbeusedtoachievehigh-speeddatatransferfromagivenperipheral.Polledinput/outputisverysimpleandcommonmethodofdatatransferwhichdoesnotrequireanyadditionallogiccircuitry.Theonlyrequirementisforanefficientprogramwhich
7、isexecutedatveryhighspeed.InterruptedIntput/outputThepollingprocedureisaformoftime-sharingwherebythefacilitiesofthecomputeraresharedbetweenanumbersofuses.Thecomputercontinuallypollseachoftheterminals,andservesaterminalforaspecifiedperiodoftimebeforemovingontothen
8、extone.Thisprocedureisinefficientbecausesystemoverheadsareincurredinpollingalltheperpheraldevicesirrespectiveoftheactualneed.Thetimeavailablefortheprocessingof
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