HT68F006 datasheet(27/93 Pages) HOLTEK

27 / 93 page

Rev. 1.00

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HT68F005/HT68F006

Enhanced I/O Flash Type MCU

HT68F005/HT68F006

Enhanced I/O Flash Type MCU

Reading Data from the EEPROM

ToreaddatafromtheEEPROM,thereadenablebit,RDEN,intheEECregistermustfirstbeset

hightoenablethereadfunction.TheEEPROMaddressofthedatatobereadmustthenbeplaced

intheEEAregister.IftheRDbitintheEECregisterisnowsethigh,areadcyclewillbeinitiated.

SettingtheRDbithighwillnotinitiateareadoperationiftheRDENbithasnotbeenset.When

thereadcycleterminates,theRDbitwillbeautomaticallyclearedtozero,afterwhichthedatacan

bereadfromtheEEDregister.ThedatawillremainintheEEDregisteruntilanotherreadorwrite

operationisexecuted.TheapplicationprogramcanpolltheRDbittodeterminewhenthedatais

validforreading.

Writing Data to the EEPROM

TowritedatatotheEEPROM,thewriteenablebit,WREN,intheEECregistermustfirstbeset

hightoenablethewritefunction.TheEEPROMaddressofthedatatobewrittenmustthenbe

placedintheEEAregisterandthedataplacedintheEEDregister.IftheWRbitintheEECregister

isnowsethigh,aninternalwritecyclewillthenbeinitiated.SettingtheWRbithighwillnotinitiate

awritecycleiftheWRENbithasnotbeenset.AstheEEPROMwritecycleiscontrolledusingan

internaltimerwhoseoperationisasynchronoustomicrocontrollersystemclock,acertaintimewill

elapsebeforethedatawillhavebeenwrittenintotheEEPROM.Detectingwhenthewritecycle

hasfinishedcanbeimplementedeitherbypollingtheWRbitintheEECregisterorbyusingthe

EEPROMinterrupt.Whenthewritecycleterminates,theWRbitwillbeautomaticallyclearedto

zerobythemicrocontroller,informingtheuserthatthedatahasbeenwrittentotheEEPROM.The

applicationprogramcanthereforepolltheWRbittodeterminewhenthewritecyclehasended.

Write Protection

Protectionagainstinadvertentwriteoperationisprovidedinseveralways.Afterthedevices

arepowered-ontheWriteEnablebitinthecontrolregisterwillbeclearedpreventinganywrite

operations.Alsoatpower-ontheBankPointer,BP,willberesettozero,whichmeanthatData

MemoryBank0willbeselected.AstheEEPROMcontrolregisterislocatedinBank1,thisaddsa

furthermeasureofprotectionagainstspuriouswriteoperations.Duringnormalprogramoperation,

ensuringthattheWriteEnablebitinthecontrolregisterisclearedwillsafeguardagainstincorrect

writeoperations.

EEPROM Interrupt

TheEEPROMwriteorreadinterruptisgeneratedwhenanEEPROMwriteorreadcyclehasended.

TheEEPROMinterruptmustfirstbeenabledbysettingtheDEEbitintherelevantinterruptregister.

WhenanEEPROMwritecycleends,theDEFrequestflagwillbeset.IftheglobalandEEPROM

interruptsareenabledandthestackisnotfull,ajumptotheassociatedInterruptvectorwilltake

place.WhentheinterruptisservicedtheEEPROMinterruptflagwillbeautomaticallyreset.More

detailscanbeobtainedintheInterruptsection.

Programming Considerations

CaremustbetakenthatdataisnotinadvertentlywrittentotheEEPROM.Protectioncanbe

enhancedbyensuringthattheWriteEnablebitisnormallyclearedtozerowhennotwriting.Also

theBankPointercouldbenormallyclearedtozeroasthiswouldinhibitaccesstoBank1where

theEEPROMcontrolregisterexist.Althoughcertainlynotnecessary,considerationmightbegiven

intheapplicationprogramtothecheckingofthevalidityofnewwritedatabyasimplereadback

process.

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