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1
Introduction to Embedded System DesignProfessor Dhananjay V. GadreElectronics and Communication EngineeringNetaji Subhas University of TechnologyBadri SubudhiElectrical Engineering DepartmentIndian Institute of Technology, JammuLecture 04Modular Approach to Embedded System Design (Continued)Welcomeback.Sowearegoingtoresumeourdiscussionsandwearegoingtoconsideranotherclassificationofmicrocontrollersormicroprocessor.Andthisoneiscalledinstructionsetarchitecture.Asthetermsuggeststheclassification,thetypesofmicroprocessorsareoftenclassifiedinthewaytheinstructionsaredesignedforagivenmicroprocessor.Nowtounderstandthatletusfirstofalldescribewhatareinstructionsandall that.(Refer Slide Time: 01:04)Now,whatareyougoingtowriteinthememoryofthemicroprocessorisaprogram.Andwhatisaprogram?Aprogramisasequenceofinstructions.OftentimeswhenIaskedthisthemeaningofaprogrampeoplementionsitisaprogramisasetofinstructions.Thatiswrongbecausesetcanberearrangedanditwouldnotbethesameprogram.Sothecorrectdefinition is a program is a sequence of instructions.Therefore,whatisaninstruction?Aninstructionisthelowestlevelatomiccommandthataprocessorunderstands.Whatdoesaninstructionconsistof?Itconsistsof2things.Thefirstpartoftheinstructioniscalledtheop-code.Thisindicatesthebasicoperationthatthe
instructionisgoingtoperform.Andthesecondpartistheoperandmeaningwhatisitgoingto work on.Forexample,anop-codecouldbetoperformanadditionandsotheop-codereferstoadd.Operandiswhatisitgoingtoadd?Isitgoingtoadd2numbers?Howarethe2numbersspecified?Arethe2numberspartofarestoredin2registersortheformatcouldbeAddR1,R2,R3.Ifitisofthefirsttype,itmeansthatR1getsthevalueofR1plusR2.Andinthesecond type, it could mean that R1 gets the value of R2 plus R3.Whetheritisofthefirsttypeorsecondtypewouldhavealotofbearingonthesizeoftheinstruction.Butneedlesstosay,theoperationtobeperformedisdescribedastheop-code.Andtheoperationtobeperformedonwhatnumbersistheoperandpartoftheinstruction.Andthisiswherethingscantakelargevarietyleadtodifferenttypesofinstructionsetarchitecture. And before we go to that, let me also classify the instructions.(Refer Slide Time: 04:01)Thetypesofinstructionsbroadlycanbeclassifiedin4typesofinstructions.ThefirstinstructionreferstowhatiscalledasDataTransferInstructions.Asthenamesuggests,theseinstructionsdealwithmovingdatafromonestoragelocationtoanotherstoragelocationinamicroprocessor or in a computer system.Whataretheselocations?Theselocationsare,couldberegisters.Theycouldbememoryandtheycouldbeports.Andso,youwouldwanttomovedatabetweentheseentities.Soinstructionsthatmovedatabetweentworegisterswouldbeavailable.Instructionsthatmovedata between registers and memory location would also be available.