使用双模式24LC21串行EEPROM

TheMicrochipTechnologyInc.24LC21isa1K-bit

(128x8)dualmodeserialEEPROMthatwas

developedprimarilyforuseincomputermonitors.This

partwasdevelopedwithinputsfromseveralcomputer

monitormanufacturers,inaccordancewiththeVESA



(VideoElectronicsStandardsAssociation)monitor

committee.Thiscommitteehasdevelopedaserial

communicationprotocolcalledDataDisplayChannel

(DDC



)whichwascreatedtoeliminatetheneedto

changedipswitcheswhenconfiguringanewsystem

oraddinganewmonitororvideocard.The24LC21

deviceisusedinthemonitortostoreandtransmitthe

EDID(extendeddisplayID)tablewhichcontainsall

set-upparametersneededbythevideocardto

operatewithaparticularmonitor.Withthissystem,the

usercannowpluganycompatiblemonitorintoany

compatiblegraphicsboardandthegraphicsboardwill

automaticallyknowwhattypeofmonitorisbeingused

andconfigureitselfaccordingly.Thisautomatic

configurationisthecornerstoneforMicrosoft



’s‘Plug

andPlay’capabilitybeingbuiltintothenew

‘Windows95



’release.AN610Usingthe24LC21DualModeSerialEEPROMTRANSMITONLYMODE(DDC1)Author:BruceNegleyMemoryProductsDivisionThe24LC21willalwayspower-upinthetransmitonlymode.Inthismode,the24LC21willoutputonebitofdataattheSDApinforeveryrisingedgeontheVCLKINTRODUCTIONpin.Thedatawillbetransmittedin8-bitwords,with