Reducingpowerconsumptionisalwaysdesirablein
systemswhereresourcesmaybelimited.Thisis
particularlytrueinUSBsystems,wheredesignersmust
notonlyunderstandtherulesimposedbytheUSB
specification,butknowwhenandhowtousewhichof
theavailablepower-savingfeatures.
Thisapplicationnotediscusseswaystomanagepower
onthemembersofthePIC18familyofmicrocontrollers
withnanoWatttechnologyinUSBapplications.Inthis
document,wewillpresentasummaryoftheUSB
specificationinregardstopowermanagementanddis-
tributionandtodescribewhenandhowtouse
power-savingfeaturesinresponsetodifferentUSB
events.Wewillalsodiscusshowtheadvanced
power-savingfeaturesofenhancedPIC18deviceswith
nanoWatttechnologycanbeusedtomeetthesegoals.
OurfocusinthisdocumentisonPIC18devices
withtheUSBperipheralandusesthe
PIC18F2455/2550/4455/4550familyofmicro-
controllersasanexample.Allreferencestothedevice
datasheetinthisdocumentrefertothedatasheetfor
thisfamily(DS39632).AN950PowerManagementforPIC18USBMicrocontrollerswithnanoWattTechnologyAuthor:RawinRojvanitThisdiscussionislimitedtoUSBdevicesonlyandisnotintendedforaUSBhost.TheauthorassumesthattheMicrochipTechnologyInc.readershavesomebasicknowledgeabouttheUSBstandard.AllreferencestotheUSBspecificationinthisINTRODUCTIONdocumentreferto“USBSpecification
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