C指令读取内部程序存储器的内容除上表功能外，还禁止程序校验除以上功能外，同时禁止外部执行保护类型
当LB1被编程时，在复位期间，EA端的电平被锁存，如果单片机上电后一直没
f沈阳航空工业学院电子工程系毕业设计（外文翻译）
有复位，锁存起来的初始值是一个不确定数，这个不确定数会一直保存到真正复位位置。为了使单片机正常工作，被锁存的EA电平与这个引脚当前辑电平一致。机密位只能通过整片擦除的方法清除。
Descriptio
6
fTheAT89C51isalowpowerhighperforma
ceCMOS8bitmicrocomputerwith4KbytesofFlashprogrammablea
derasablereado
lymemoryPEROMThedeviceisma
ufacturedusi
gAtmel’shighde
sity
o
volatilememorytech
ologya
discompatiblewiththei
dustrysta
dardMCS51i
structio
seta
dpi
outTheo
chipFlashallowstheprogrammemorytobereprogrammedi
systemorbyaco
ve
tio
al
o
volatilememoryprogrammerBycombi
i
gaversatile8bitCPUwithFlasho
amo
olithicchiptheAtmelAT89C51isapowerfulmicrocomputerwhichprovidesahighlyflexiblea
dcosteffectivesolutio
toma
yembeddedco
trolapplicatio
s
Fu
ctio
characteristic
TheAT89C51providesthefollowi
gsta
dardfeatures4KbytesofFlash128bytesofRAM32IOli
estwo16bittimercou
tersafivevectortwoleveli
terruptarchitectureafullduplexserialporto
chiposcillatora
dclockcircuitryI
additio
theAT89C51isdesig
edwithstaticlogicforoperatio
dow
tozerofreque
cya
dsupportstwosoftwareselectablepowersavi
gmodesTheIdleModestopstheCPUwhileallowi
gtheRAMtimercou
tersserialporta
di
terruptsystemtoco
ti
uefu
ctio
i
gThePowerdow
ModesavestheRAMco
te
tsbutfreezestheoscillatordisabli
gallotherchipfu
ctio
su
tilthe
exthardwarereset
Pi
Descriptio
VCC：SupplyvoltageGND：Grou
dPort0：
Port0isa
8bitope
drai
bidirectio
alIOportAsa
outputporteachpi
ca
si
keightTTLi
putsWhe
1sarewritte
toport0pi
sthepi
sca
beusedashighimpeda
cei
putsPort0mayalsobeco
figuredtobethemultiplexedloworderaddressdatabusduri
gaccessestoexter
alprograma
ddatamemoryI
thismodeP0hasi
ter
alpullupsPort0alsoreceivesthecodebytesduri
gFlashprogrammi
ga
doutputsthecodebytesduri
gprogramverificatio
Exter
alpullupsarerequiredduri
gprogramverificatio
Port1
f沈阳航空工业学院电子工程系毕业设计（外文翻译）
Port1isa
8bitbidirectio
alIOportwithi
ter
alpullupsThePort1outputbuffersca
si
ksourcefourTTLi
putsWhe
1sarewritte
toPort1pi
stheyarepulledhighbythei
ter
alpullupsa
dca
beusedasi
putsAsi
putsPort1pi
sthatareexter
allybei
gpulledlowwillsourcecurre
tIILbecauseofthei
ter
alpullupsPort1alsoreceivestheloworderar
