驱动互补LED
LightEmittingDiodes,orLED's,arediscretecompo-nentsabletoproducelightwhenacurrentpasses
throughthem.Mostmicrocontrollerdesignsuseoneor
moreLED's.Thisapplicationhighlightstheutilityof
drivingmultipleLED'swithaminimumnumberofI/O
pins.Typically,eachI/OdrivesorsourcesasingleLED.
Todrivemorethanone,ahighI/Ocountisrequired.In
ordertoreduceI/Orequirements,LED'saremulti-plexedinamatrix(asfoundonakeyboard).Thecom-plementaryLEDdrivemethodproposestoimplement
evenmoreLEDswhileusingfewerI/O.
LEDsarepolarizedandcanonlyoperatewhencurrent
flowsfromanodetocathode(unlikeaswitch).Wecan
thereforetakeadvantageofthisfact.Table1showsthe
numberofpossibleLEDswithrespecttothenumberof
I/Opinsrequired.Fifty-sixLEDscanbedrivenusing
only8pins.TheonlydrawbackisthatonlyoneLEDcan
bedrivenatatime.
MTB029ComplementaryLEDDriveTHEORYOFOPERATIONAuthor:Jean-ClaudeRebicPioneer-StandardSomemicrocontrollersavailabletodaycansinkhighcurrent,whileothersofferalimitednumberofpinstosourcehighcurrent.MicrochipmicrocontrollershaveaINTRODUCTIONveryexiblepinstructure.Whenapinisconguredasaninput,th
