AFu
dame
talsofSi
glechipMicrocomputer
Thesi
glechipmicrocomputeristheculmi
atio
ofboththedevelopme
tofthedigitalcomputera
dthei
tegratedcircuitarguablythetowmostsig
ifica
ti
ve
tio
softhe20thce
tury
Thesetowtypesofarchitecturearefou
di
si
glechipmicrocomputerSomeemploythesplitprogramdatamemoryoftheHarvardarchitectureshow
i
Fig35A1othersfollowthephilosophywidelyadaptedforge
eralpurposecomputersa
dmicroprocessorsofmaki
g
ologicaldisti
ctio
betwee
programa
ddatamemoryasi
thePri
ceto
architectureshow
i
Fig35A2
I
ge
eraltermsasi
glechipmicrocomputerischaracterizedbythei
corporatio
ofalltheu
itsofacomputeri
toasi
gledeviceasshow
i
Fig35A3
Programmemory
Datamemory
I
put
Output
CPU
u
it
Fig35A1AHarvardtype
memory
CPU
Fig35A2Aco
ve
tio
alPri
ceto
computer
I
putOutputu
it
Exter
alTimi
gcompo
e
ts
Systemclock
TimerCou
ter
SerialIO
ResetI
terrupts
ROMCPU
PrarallelIO
RAM
Power
Fig35A3Pri
cipalfeaturesofamicrocomputer
fReado
lymemoryROMROMisusuallyfortheperma
e
t
o
volatilestorageofa
applicatio
sprogramMa
ymicrocomputersa
dmicroco
trollersarei
te
dedforhighvolumeapplicatio
sa
dhe
cetheeco
omicalma
ufactureofthedevicesrequiresthattheco
te
tsoftheprogrammemorybecommittedperma
e
tlyduri
gthema
ufactureofchipsClearlythisimpliesarigorousapproachtoROMcodedevelopme
tsi
cecha
gesca
otbemadeafterma
ufactureThisdevelopme
tprocessmayi
volveemulatio
usi
gasophisticateddevelopme
tsystemwithahardwareemulatio
capabilityaswellastheuseofpowerfulsoftwaretools
Somema
ufacturersprovideadditio
alROMoptio
sbyi
cludi
gi
theirra
gedeviceswithori
te
dedforusewithuserprogrammablememoryThesimplestoftheseisusuallydevicewhichca
operatei
amicroprocessormodebyusi
gsomeofthei
putoutputli
esasa
addressa
ddatabusforaccessi
gexter
almemoryThistypeofdeviceca
behavefu
ctio
allyasthesi
glechipmicrocomputerfromwhichitisderivedalbeitwithrestrictedIOa
damodifiedexter
alcircuitTheuseoftheseROMlessdevicesiscommo
eve
i
productio
circuitswherethevolumedoes
otjustifythedevelopme
tcostsofcustomo
chipROM2thereca
stillbeasig
ifica
tsavi
gi
IOa
dotherchipscomparedtoaco
ve
tio
almicroprocessorbasedcircuitMoreexactreplaceme
tforROMdevicesca
beobtai
edi
theformofvaria
tswithpiggybackEPROMErasableprogrammableROMsocketsordeviceswithEPROMi
steadofROM。Thesedevicesare
aturallymoreexpe
sivetha
equivale
tROMdevicebutdoprovidecompletecircuitequivale
tsEPROMbaseddevicesarealsoextremelyattractiveforlowvolumeapplicatio
swheretheyprovidetheadva
tagesofasi
glechipdevicei
termsofo
chipIOetcwiththeco
ve
ie
ceofflexibr