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Intel MCS 51 User Manual

Intel MCS 51
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i~o
83C152 HARDWAREDESCRIPTION
In the secondprocedure,an initiahzingstation asksfor
an address assignmentfrom the system.This requires
that somestation on the link take care of the task of
maintaininga recordof whichaddressesare used.This
station will be called station-1.When the initialing
station,called station-2,getson the link,it sendsout a
messagewith a broadcast address. The format of the
messageshould be such that all other stations on the
link recognizeit as a request for address assignment.
Part ofthe measagefromstation-2is a randomnumber
generatedby the station requestingthe addreas. Sta-
tion-2then examinesall receivedmessagrafor this ran-
domnumber.Therandomnumbercouldbe the addreas
ofthe receivedmessageor couldbe withinthe informat-
ion sectionof a broadcastframe.All the stations, ex-
cept station-1,on the link shouldignorethe initializa-
tion request.Station-1,uponreceivingthe initialization
request,assignsan addreasand returns it to station-2.
Station-1willberequiredto formatthe messagein such
a mannerso that all stationson the linkrecogniseit as
a responseto initialization.Thismeansthat all stations
exceptstation-2ignorethe return message.
3.5.6
TEST MODES
Thereare twotest modes
associatedwiththe GSCthat
are made available to the user. The test modes are
named Raw Receive and Raw Transmit. The teat
modes are selected by the proper setting of the two
mode bits in GMOD (MO = GMOD.5, Ml =
GMOD.6).If MI,MO = 0,1th.mRawTransmit is se-
lected.If M1,MO= 1,0then Raw Receiveis enabled.
The 32-bit CRC cannot be used in any of the teat
modes,or else CRCerrors willoccur.
In RawTransmit,the transmitoutputis internallycon-
nected to the Receiver input. This is intended to be
used as a local loopback test mode,so that all data
written to the transmitter will be returned by the rc-
ceiv~. -W Transmitm &Obe usedto t
ransmituser
&ta. If Raw Transmi
t is used in this way the data is
emittedwith no preamble,flag,address,CRC, and no
bit insertion.The data is still encodedwith whatever
formatisselected,ManchesterwithCSMA/CD,NRZI
with SDLCor as NRZ if externalclocksare used.The
receiverstill operatesas normaland in this modemost
of the receivefunctionscartbe tested.
In Raw Receive,the transmitter shouldbe externally
connectedto the receiver.To dothis a port pin should
beusedto enablean externaldeviceto connectthe two
pinstogether.In Raw Receivemodethe receiveracts as
normal except that all bytes followingthe BGF are
londedintothe receiveFIFO, includingthe CRC. Also
addressrecognitionis not activebut needs to be per-
formedin software.If SDLCisselectedas the protocol,
zero-bitdeletion is still enabled.The transmitter still
operatesasnormal and in this modemost of the trans-
mitterfunctionsand an externaltransca
“Vercan be teat-
ed.This is alsothe onlywaythat the CRC can be read
bythe CPU, but the CRC error bit willnot be set.
3.5.7
EXTERNAL DRIVER INTERFACE
A signalis providedfrom the C152to enabletranstnit-
ter driversfor the serial link. This is providedfor sys-
tems that require more than what the GSC ports are
capableofdelivering.The voltageand currents that the
GSCiscapableofprovidingare the samelevelsas those
fornonnal port operation.Thesignalusedto enablethe
externaldriversis~. Nosimilarsignalis neededfor
the receiver.
~ is activeone bit time &fore transmissionbegins.
In C3MA/CD ~ remains
activefor two bit times
after the CRC is transxm
‘tted.In SDLC~ remains
activeuntil the last bit of the EOFis transmitted.
3.5.8 JITTER(RECEIVE)
Datajitter isthe differencebetweenthe actual transmitt-
ed waveform and the exact calculated value(s). In
NRZI, datajitter wouldbe howmuchthe actual wave-
formexceedsor fallsshort ofonecalculatedbit time.A
bittimeequalsI/baud rate. If usingManchesterencod-
ing,there canbe two transitionsduringone bit time as
shownin Figure 3.11.This causesa seumd parameter
to beconsideredwhentryingto figureout the cctmplete
&ta jitter amount.This other parameteris the half-bit
jitter. Thehsdf-bitjitter iscomprisedofthe differencein
timethat the half-bittransitionactuallyoccursand the
calcrdatedvalue.Jitter isimportantbecauseif the tran-
sitionoccurstoo soonit is considerednoise,and if the
transitionoccurs too
late, then either the bit is missed
or a collisionis assumed.
7-36

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Intel MCS 51 Specifications

General IconGeneral
BrandIntel
ModelMCS 51
CategoryMicrocontrollers
LanguageEnglish

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