int&
83C152 HARDWARE DESCRIPTION
2.8 Power DownandIdle
Both
of these operationsfunctionidenticallyas in the
80C51BH.ApplicationNote 252,“Deaigningwith the
SOC51BH”givesan excellentexplanationon the use of
the reducedpower consumptionmodes.Some of the
itemsnotcoveredin AP-252are the cxmsiderationsthat
are applicablewhen using the GSC or DMA in con-
junctionwith the powersavingmodea.
The GSC continuesto operate in Idle ss long as the
interrupts are enabled.The interrupts need to be en-
abled,sothat the CPUcan seMce theFIFO’S.In order
to properlytetminate a reception or transmissionthe
C152must not be in idle whenthe EOFis transmitted
or received.After servicingthe GSC,usersoftwarewill
need to again invokethe Idle comman
d as the CPU
does not automatically re-enter the Idle mode after
servicingthe interrupts.
TheGSCdoesnot operatewhileitsPowerDownsothe
steps requiredprior to entering PowerDowtsbecome
more complicated.The sequencewhenenteringPower
Downand the strstusof the I/O is ofmajorimportance
in preventingdamageto the C152or othercomponents
in the system.Sincethe onlywayto exitPowerDown
is witha R- severalproblemareas becomeverysig-
nificant.Someof the problemsthat merit carefsdcon-
siderationare caseswherethe PowerDownoccursdur-
ing the middle of a transmission,and the possibility
that other stations are not or cannot enter this same
mode.The state of the GSC1/0 pins becomescritical
and the GSCstatus willneedto te savedbeforepower
downis entered.There willalso needto besomemeth-
od ofidentifyingto the CPUthat the followingReaetis
probablynota coldstart and that other stationson the
link mayhavealreadybeeninitialized.
The DMA circuitry stops operation in both Idle and
PowerDownmodes.Sin= operationisstoppedin both
mod- the prcesa shouldbe similarin each case. Spe-
cificstepsthat needto be taken include:notificationto
otherdevicesthat DMA operationis aboutto ceasefor
a particular station or network, proper withdrawal
from DMA operation, and saving the status of the
DMAchannels.Again,the status of the 1/0 pins dur-
ing PowerDown needs careful considerationto avoid
damageto the C152or other components.
Port 4 returns to its input sta~ which is high l=el
using
Wtzlk pllhp devices.
2.9 LocalSerialChannel
The Local SerialChannel(LSC)is the name givento
the UART that exists on all MCS-51devices. The
LSC’Sfunctionand operationis exactlythe sameas on
the 80C51BH.For a descriptionon the useofthe LSC,
refer to the 8051/52HardwareDescriptionChapter in
the IntelEmbeddedControllerHandbook,underserial
Interface.
3.0 GLOBALSERIALCHANNEL
3.1Introduction
The GlobalSerial Channel(GSC)is a multi-protocol,
highperformanceserialinterfacetargetedfordata rates
up to 2 MBPS with on-chipclock recovery,and 2.4
MBPSusingthe externalclockoptions.In applications
usingthe serialchannel,the GSCimplementsthe Data
LinkLayerandPhysicalLinkLayerasdescribedin the
1S0 referencemodelfor opensystemsinterconnection.
The GSC is designedto meet the requirementsof a
widerangeofserialcommunicationsapplicationsandis
optimised to implement Carrier-SenseMulti-Access
with CollisionDetection (CSMA/CD) and Synchro-
nous Data Link Control (SDLC)protocols.The GSC
architectureis alsodesignedto provideflexibilityinde-
ftig non-standardprotocols.Thisprovidesthe ability
to retrofit newproducts into older serial technologies,
as wellas the developmentof proprietaryinterconnect
schemesfor serial backplaneenvironments.
The versatilityofthe GSCis demonstratedby the wide
range of choices available to the user. The
VariOUS
modes
of operation are summarizedin Table 3.1. In
subsequentsections,each availablechoiceof operation
willbe explainedin detail.
In usingTable 3.1,the parameterslistedvertically(on
the left hand side) representan optionthat is selected
(X). The parameters listedhorizontally(alongthe top
of the table)are all the parametersthat couldtheoreti-
cally be selected (Y). The symbolat the junction of
bothX andY determinesthe applicabilityofthe option
Y.
Note,that notallcombinationsarebackwardscompati-
ble. For example,Manchester encodingrequires half
duplex,but half duplex does not require Manchester
encoding.
7-17
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