Communication Interface of The Embedded Systems

Communication Interface

1. COMMUNICATION INTERFACE
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2. Types:
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1. Onboard Communication Interfaces
a.I2C Bus
b.SPI Bus
c.UART
d.1-Wire Interface
e.Parallel Interface
2. External Communication Interfaces
a.RS-232 C
b.USB
c.Fire wire
d.IrDA
e.Bluetooth
f.Wi-Fi
g.ZigBee

3. 1.Onboard Communication Interfaces
(Device/Board level Communication Interfaces):
a)InterIntegratedCircuit(I2C)Bus:
Itisasynchronousbi-directionalhalf-duplextwowireserial
interfacebus.
–TheI2Cbuscompriseoftwobuslines:
•SerialClock(SCLline)–responsibleforgeneratingsynchronization
clockpulses
•SerialData(SDAline)–responsiblefortransmitting
–I2CbusisasharedbussystemtowhichmanynumberofI2Cdevicescanbe
connected.DevicesconnectedtotheI2Cbuscanactaseither'Master'or
'Slave’.
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•The'Master'deviceisresponsibleforcontrollingthecommunication.
•'Slave'deviceswaitforthecommandsfromthemasterandrespond.
•Thesynchronizationclocksignalisgeneratedbythe'Master'deviceonly.
•I2Csupportsmultimastersonthesamebus
•Boththebuslinesshouldbepulledtothesupplyvoltageusingpull-up
resistors.Thetypicalvalueofresistorsusedinpull-upis2.2K.

5. The sequence of operations for communicating
with an I2C slave device is listed below:
•Themasterdevicepullstheclockline(SCL)to'HIGH'
•Themasterdevicepullsthedataline(SDA)'LOW
•Themasterdevicesendstheaddressofthe‘slave’
•ThemasterdevicesendstheReadorWritebit
•Themasterdevicewaitsfortheacknowledgementbitfromtheslave
device
•Theslavedevicewiththeaddressrequestedbythemasterdevice
respondsbysendinganacknowledgebit(Bitvalue1)overtheSDAline
•Uponreceivingtheacknowledgebit,theMasterdevicestartsthe
communication.
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6. b)SerialPeripheralInterface(SPI)Bus:
–TheSerialPeripheralInterfaceBus(SPI)isa
synchronousbi-directionalfullduplexfour-wireserial
interfacebus.
–TheconceptofSPIwasintroducedbyMotorola.
–SPIisasinglemastermulti-slavesystem.
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SPI requires four signal lines for communication. They are:
•Master Out Slave In (MOSI) –Signal line carrying the data from master to slave
device. It is also known as Slave Input/SIave Data In (SI/SDI)
•Master In Slave Out (MISO) –Signal line carrying the data from slave to master
device. It is also known as Slave Output (SO/SDO)
•Serial Clock (SCLK) –Signal line carrying the clock signals
•Slave Select (SS) –Signal line for slave device select. It is an active low signal

8. •Masterselectstherequiredslavedevicebyassertingthe
correspondingslaveselectsignal'LOW’.
•TheserialdatatransmissionthroughSPIbusisfullyconfigurable
•SPIdevicescontainacertainsetofregisterswhichareSerial
peripheralcontrolregister&statusregister
•SPIworksontheprincipleof'ShiftRegister’
•Themasterandslavedevicescontainaspecialshiftregisterforthe
datatotransmitorreceive.
•Theshiftregistersof'master'and'slave'devicesformacircular
buffer
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9. c)Universal Asynchronous Receiver Transmitter (UART):
–UniversalAsynchronousReceiverTransmitter(UART)baseddatatransmissionisan
asynchronousformofserialdatatransmission.
–Itdoesn'trequireaclocksignaltosynchronizethetransmittingendandreceiving
endfortransmission.
–Insteaditreliesuponthepre-definedagreementbetweenthetransmittingdevice
andreceivingdevice.
–Theserialcommunicationsettingsforbothtransmitterandreceivershouldbesetas
identical.
–Thestartandstopofcommunicationisindicatedthroughinsertingspecialbitsinthe
datastream.
–Ifparityisenabledforcommunication,thetransmittingdeviceaddsaparitybit.This
isforerrorchecking
–TheUARTofthereceivingdevicediscardsthe'Start','Stop'and'Parity’bit
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11. d)1-Wire Interface:
•1-wire interface is an asynchronous half-duplex communication
protocol developed by Maxim Dallas Semiconductor
•It makes use of only a single signal line (wire) called DQ
•One of the key features of 1-wire bus is that it allows power to be sent
•Every 1-wire device contains a unique 64bit identification number stored
within it.
•The identifier has three parts: an 8 bit family code, a 48 bit serial number
and an 8 bit CRC.
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12. The sequence of operation for communicating with a 1-wire slave device is listed
below:
•Themasterdevicesendsa'Reset'pulseonthe1-wirebus.
•Theslavedevice(s)respondwitha'Presence'pulse.
•ThemasterdevicesendsaNetAddressCommandfollowedbythe64-bit
addressofthedevice.
•Themasterdevicesendsaread/writefunctioncommandbit.
•ThemasterinitiatesaReaddata/Writedatafromthedeviceortothedevice
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13. e)Parallel Interface:
•Theon-boardparallelinterfaceisusedforcommunicatingwith
peripheraldeviceswhicharememorymappedtothehostofthesystem
•Thecommunicationthroughtheparallelbusiscontrolledbythecontrol
signalinterface
•Onlythehostprocessorhascontroloverthe'Read'and'Write'control
signals.
•Theexternaldeviceisnormallymemorymappedtothehostprocessor
andarangeofaddressisassignedtoit.
•Whentheaddressselectedbytheprocessor,theprocessorthencanread
orwritefromortothedevicebyassertingthecorrespondingcontrolline
(RD\andWR\respectively).
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15. COMMUNICATION INTERFACE
2.External Communication Interfaces
(Product level Communication Interfaces):
a)RS-232 C:
RecommendedStandardnumber232,revisionCisafullduplex,wired,
asynchronousserialcommunicationinterface.RS-232supportstwo
differenttypesofconnectors:
•DB-9:9-Pinconnector
•DB-25:25-Pinconnector
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16. •TheRS-232interfacedefinesvarioushandshakingandcontrolsignalsforcommunication
•ThereareDataTerminalEquipment(DTE)andDataCommunicationEquipment(DCE)inRS
232.
•Ifnodataflowcontrolisrequired,onlyTXDandRXDsignallinesandgroundline(GND)are
requiredfordatatransmissionandreception.
•Ifhardwaredataflowcontrolisrequiredforserialtransmission,variouscontrolsignallines
oftheRS-232connectionareusedappropriately.
•TheRequesttoSend(RTS),ClearToSend(CTS),DataTerminalReady(DTR)andDataSet
Ready(DSR)signalsco-ordinatethecommunicationbetweenDTEandDCE.
•AspertheEIAstandardRS-232Csupportsbaudratesupto20Kbps(Upperlimit19.2Kbps)
•Thecommonlyusedbaudratesbydevicesare300bps,1200bps,2400bps,9600bps,
11.52Kbpsand19.2Kbps.
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17. b)Universal Serial Bus (USB):
•Universal Serial Bus (USB) is a wired high-speed serial bus for
data communication.
•The USB communication system follows a star topology with a USB
host at the Centre and one or more USB peripheral devices/USB
hosts connected to it.
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18. •USB transmits data in packet format
•The USB communication is a host initiated one.
•The USB host contains a host controller
•The physical connection between a USB peripheral device
and master device is established with a USB cable which
supports communication distance of up to 5 metres
•USB interface has the ability to supply power to the
connecting devices
•It can supply power up to 500 mA at 5 V.
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19. USBsupportsfourdifferenttypesofdatatransfers
–Controltransfer:UsedbyUSBsystemsoftware
–Bulktransfer:Usedforsendingablockofdata
–Isochronousdatatransfer:Usedforreal-timedata
communication.
–Interrupttransfer:Usedfortransferringsmallamountof
data
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20. c)IEEE 1394 (Fire wire):
–IEEE 1394 is a wired, isochronous high-speed serial communication bus.
–It is also known as High Performance Serial Bus (HPSB). It supports 400-
3200Mbps data rate.
–The interface cable supports 3 types of connectors, namely; 4-pin connector, 6-pin
Connector (alpha connector) and 9 pin connector (beta connector).
–The 6 and 9 pin connectors carry power.
–IEEE 1394 doesn't require a host for communicating between devices.For example,
you can directly connect a scanner with a printer for printing
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21. COMMUNICATION INTERFACE
2.External Communication Interfaces
(Product level Communication Interfaces):
d)Infrared (IrDA):
• Infrared(IrDA)isaserial,halfduplex,lineofsight
basedwirelesstechnologyfordatacommunication.
•Infraredcommunicationtechniqueusesinfraredwavesofthe
electromagneticspectrumfortransmittingthedata.
•Itsupportspoint-pointandpoint-to-multipointcommunication
•ThecommunicationrangeforIrDAliesintherange10cmto1
m.
•IRsupportsdataratesrangingfrom9600bits/secondto
16Mbps.
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22. Depending on the speed of data transmission IR is
classified into:
Serial IR (SIR) –supports data rates ranging from 9600bps to 115.2kbps.
Medium IR (MIR) –supports data rates of 0.576Mbps and 1.152Mbps.
Fast IR (FIR) –supports data rates up to 4Mbps.
Very Fast IR (VFIR) –supports high data rates up to 16Mbps.
Ultra Fast IR (UFIR) –targeted to support a data rate up to 100Mbps
IrDA communication, Infrared Light Emitting Diode (LED) is the IR
source for transmitter and at the receiving end a photodiode acts as
the receiver.
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23. e)Bluetooth(BT):
–Bluetoothisalowcost,lowpower,shortrangewirelesstechnology
fordataandvoicecommunication.
–Bluetoothoperatesat2.4GHzoftheRadioFrequencyspectrumand
usestheFrequencyHoppingSpreadSpectrum(FHSS)techniquefor
communication.
–Itsupportsadatarateofupto1Mbpsandarangeof30feetfordata
communication.
–Bluetoothcommunicationhastwoparts–aphysicallinkpartanda
protocolpart.
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24. –EachBluetoothdevicewillhavea48-bitunique
identificationnumber
–Bluetoothsupportspoint-to-pointandpoint-to-multipoint
wirelesscommunication.
–Thepoint-to-pointcommunicationfollowsthemaster-slave
relationship.
–Bluetoothisthefavoritechoiceforshortrangedata
communicationinhandheldembeddeddevices.
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25. f)Wi-Fi:
–WirelessFidelityisthepopularwirelesscommunication
techniquefornetworkedcommunicationofdevices.
–Wi-FifollowstheIEEE802.11standard.
–Wi-Fiisintendedfornetworkcommunicationanditsupports
InternetProtocol(IP)basedcommunication.
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26. •IPaddressandWi-Firouter/WirelessAccessPointare
requiredforWi-Fibasedcommunication.
•Wi-Firouterisresponsibleforrestrictingaccesstothe
network,assigningIPaddresstothedevices,routingdata
packetstotheintendeddevices.
•Wi-Fienableddeviceswillbehavingwirelessadaptor.
•Wi-Fioperatesat2.4GHzor5GHzofRadiospectrum.
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27. g)ZigBee:
•ZigBeeisalowpower,lowcost,wirelessnetworkcommunicationprotocol
basedontheIEEE802.15.4-2006standard.
•ZigBeeoperatesworldwideattheunlicensedbandsofRadiospectrum,mainly
at2.400to2.484GHz,902to928MHzand868.0to868.6MHz
•ZigBeesupportsanoperatingdistanceofupto100metresandadatarateof
20to250Kbps
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28. In the ZigBee terminology, each ZigBee device falls under any one
of the following ZigBee device category:
–ZigBee Coordinator (ZC)/Network Coordinator
•The ZigBee coordinator acts as the root of the ZigBee network.
–ZigBee Router (ZR)/Full function Device (FFD)
•Responsible for passing information from device to another device
or to another ZR.
–ZigBee End Device (ZED)/Reduced Function Device (RFD)
•End device containing ZigBee functionality for data
communication.
•It can talk only with a ZR or ZC and doesn't have the capability to
act as a mediator for transferring data from one device to another.
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