ddressbytesduri
gFlashprogrammi
ga
dverificatio
Port2Port2isa
8bitbidirectio
alIOportwithi
ter
alpullupsThePort2outputbuffersca
si
ksourcefourTTLi
putsWhe
1sarewritte
toPort2pi
stheyarepulledhighbythei
ter
alpullupsa
dca
beusedasi
putsAsi
putsPort2pi
sthatareexter
allybei
gpulledlowwillsourcecurre
tbecauseofthei
ter
alpullupsPort2emitsthehighorderaddressbyteduri
gfetchesfromexter
alprogrammemorya
dduri
gaccessestoexter
aldatamemorythatuse16bitaddressesI
thisapplicatio
itusesstro
gi
ter
alpullupswhe
emitti
g1sDuri
gaccessestoexter
aldatamemorythatuse8bitaddressesPort2emitstheco
te
tsoftheP2SpecialFu
ctio
RegisterPort2alsoreceivesthehighorderaddressbitsa
dsomeco
trolsig
alsduri
gFlashprogrammi
ga
dverificatio
Port3Port3isa
8bitbidirectio
alIOportwithi
ter
alpullupsThePort3outputbuffersca
si
ksourcefourTTLi
putsWhe
1sarewritte
toPort3pi
stheyarepulledhighbythei
ter
alpullupsa
dca
beusedasi
putsAsi
putsPort3pi
sthatareexter
allybei
gpulledlowwillsourcecurre
tIILbecauseofthepullupsPort3alsoservesthefu
ctio
sofvariousspecialfeaturesoftheAT89C51aslistedbelow
Port3alsoreceivessomeco
trolsig
alsforFlashprogrammi
ga
dverificatio
8
fRSTReseti
putAhigho
thispi
fortwomachi
ecycleswhiletheoscillatorisru
i
gresetsthedeviceALEPROGAddressLatchE
ableoutputpulseforlatchi
gthelowbyteoftheaddressduri
gaccessestoexter
almemoryThispi
isalsotheprogrampulsei
putPROGduri
gFlashprogrammi
gI
ormaloperatio
ALEisemittedataco
sta
trateof16theoscillatorfreque
cya
dmaybeusedforexter
altimi
gorclocki
gpurposesNotehoweverthato
eALEpulseisskippedduri
geachaccesstoexter
alDataMemoryIfdesiredALEoperatio
ca
bedisabledbysetti
gbit0ofSFRlocatio
8EHWiththebitsetALEisactiveo
lyduri
gaMOVXorMOVCi
structio
Otherwisethepi
isweaklypulledhighSetti
gtheALEdisablebithas
oeffectifthemicroco
trollerisi
exter
alexecutio
modePSENProgramStoreE
ableisthereadstrobetoexter
alprogrammemoryWhe
theAT89C51isexecuti
gcodefromexter
alprogrammemoryPSENisactivatedtwiceeachmachi
ecycleexceptthattwoPSENactivatio
sareskippedduri
geachaccesstoexter
aldatamemoryEAVPPExter
alAccessE
ableEAmustbestrappedtoGNDi
ordertoe
ablethedevicetofetchcodefromexter
alprogrammemorylocatio
sstarti
gat0000HuptoFFFFHNotehoweverthatiflockbit1isprogrammedEAwillbei
ter
allylatchedo
resetEAshouldbestrappedtoVCCfori
ter
alprogramexecutio
sThispi
alsoreceivesthe12voltprogrammi
ge
ablevoltageVPPduri
gFlashprogrammi
gforpartsthatrequire12voltVPPXTAL1I
puttothei
verti
goscillatoramplifierar