serial communication protocol

Touchpoint 4 Serial Communication Protocol Issue 1 09/07

Touchpoint 4

Serial Communication Protocol


CONTENTSINTRODUCTION 1

OVERVIEW 1 GLOSSARY 2 COMMUNICATIONPORT 2 ADDRESSSETTINGPROCEDURE 3 PROTOCOLSPECIFICS 3 Packet Length 4 Checksum 4 ACK/NAK Handshake 5 TIMEDIAGRAM 6

PROTOCOLPACKETDEFINITION 6

PACKETFORMAT 6 Start Code 6 Slave Address 6 Length 6 Command 6 Data 7 Checksum 7

GENERICDATAFORMATS 7 Date Format 7 Time Format 7 Date/Time Examples: 7 Concentration Code: 7 Concentration Data Format Code 8 Concentration Example: 8

GENERICRESPONSES 8 ACK - 0x01 8 NAK - 0x21 9 Bad Packet - 0x66 9 Unknown CMD –0x67 9

PROTOCOLCOMMANDDEFINITION 9 HANDSHAKECOMMAND–0X40 9 Command packet to instrument: 9 Example: 9 Response packet from instrument: 9 Example: 9

GETUNITANDPOINTSSTATUS-0X30 10 Command packet to instrument: 10 Example: 10 Response packet from instrument: 10 Example: 11


RESETFAULT&ALARM–0X41 12 Command packet to instrument: 12 Example: 12 Response packet from instrument: 13 Example: 13

PHYSICALLAYER 13

PREAMBLE 13 ELECTRICALINTERFACES 13 Multipoint Serial Bus Infrastructure 13 Multipoint System requirements 14 MECHANICALINTERFACES 15 Connectors pin-out 15


1

Introduction

Overview ThismanualdescribesthesetupandoperationoftheTouchpoint4SerialCommunicationprotocol.

YourTouchpoint4gasdetectorcontrollerisequippedwithaserialremotedevicecommunicationport.Withthiscommunicationport,youcanmonitortheTouchpoint4system’soperationwithmasterfromaremotelocation.Itwillalsoallowyoutogathergasconcentrationdataforanalysisorreports.

TheTouchpoint4gasdetectorcontrolleracceptscommandsandissuesresponsestoanyvalidcommanditreceives.TheTouchpoint4gasdetectorcontrollerisalwaysthe“slave”device,andtheremoteequipmentisthe“master”device.Themastercanbeapersonalcomputer(PC),aprogrammablelogiccontroller(PLC),orotherdevicecapableofRS-485serialcommunications.Thisconfigurationrequiresa“master”device.

Therefore,oneTouchpoint4gasdetectorcontrollerwillnotcommunicatedirectlywithanotherTouchpoint4gasdetectorcontroller.However,onemastercanbeusedtocommunicatewithmorethanoneTouchpoint4gasdetectorcontrollersonatwo-wireRS-485bus.

TheTouchpoint4gasdetectorcontrollersupportsmultiplebaudrates.Theseuserselectableratesare1200,2400,4800,9600,and19,200.Additionalportsettingsare8-bit,1stopbit,andnoparity.

TheslaveisidentifiedbyanaddressconfiguredintotheTouchpoint4gasdetectorcontroller(selectable1-16).EachTouchpoint4gasdetectorcontrolleronanRS-485networkmusthaveauniqueaddress.

Themasterisalwaysataddress0.EachTouchpoint4gasdetectorcontrollerwillrespondtoasignaldirectedtoitfromthemaster.Topreventacollisionofmessages,themastermustavoidtransmittinganyinformationafterapacketuntiltheslaveresponds.Touchpoint4willrespondin500ms.


Glossary

Thefollowingtermsareusedinthismanual:

Handshake:Theprocessofacknowledgingacommunicationhasbeenreceived.TheTouchpoint4gasdetectorcontrollerusesACK/NAKresponses.

Hexadecimal:Atypeofnumberingsystemwithabaseof16.Inthisnumericalsystem,thelettersAthroughFrepresentsnumbers10through15respectively.Forexample,3Finhexadecimalrepresents63indecimal.Theshortenedversionofthewordhexadecimalisgenerally"Hex",asin"Hex3F.""0x"isthenotationusedinthismanualforhexadecimal(e.g.0x3F).

Instrument:ThistermisusedtorefertotheTouchpoint4gasdetectorcontroller.

Master:AcomputerorPLCthatcommunicateswithslavesusingtheTouchpoint4protocol.

Packet:Ablockofinformationthatispassedbetweenthemasterandtheslave.Apacketismadefrommanybytesofinformation.

Protocol:Themannerinwhichdataistransferredandtheformatusedforthetransfer.Touchpoint4protocolreferstothepacketsoftransferreddatatheTouchpoint4instrumentrecognizes.

Slave:Touchpoint4gasdetectorcontroller.Anetworkmayhaveseveralslaves.

Time-Out:Themaximumamountoftimeallowedbetweenthetimethelastbyteofapacketissentfromthe“master”devicetothetimethe“slave”deviceresponds.Thetime-outperiodof1secondisrecommendedforthisprotocol.Infact,theperiodfromrequesttransmissiontoresponsereceptionisnotmorethan500ms.

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3

Communication Port

AccesstotheTouchpoint4protocolisthroughtheterminalblockonthecommonmoduleofTouchpoint4gasdetectorcontroller.ThisportisdesignedforbidirectionalcommunicationsbetweentheTouchpoint4instrumentandyourmaster.

SignalspresentattheportconformtoRS-485specifications.Thepin-outspecificationsaredescribedinthechapterconnectors pin-out.

Address Setting Procedure

Afterthenetworkingcablinghasbeenconnectedtotheslave,theslavemustbeconfiguredtocommunicate.Baudrateandaddressareselectable.Configurationisperformedwiththefollowingsequence:

1. AccessthemenusystemandselecttheRS485 communication link settingsmenuoption.PressUP/DOWN,theiconflashes.

2. PressOK,thecontroller’scurrentaddressisdisplayed.

3. UseUP/DOWNtochangetheaddress(between1and16available).

4. PressOKtoacceptthechange. Thedisplaychangestodisplaythecurrentbaudrate.

5. UseUP/DOWNtochangethebaudrate(1200,2400,4800,9600, 19200available).

6. PressOKtoacceptthechange.

PleaserefertotheTechnicalManualformoredetails.

Protocol Specifics

Theprotocolhasbeendesignedforflexibilityandefficiency.Thisbyte-wiseprotocolcommunicatesinformationbytransferringbytesofdatabackandforthbetweenmasterandslave.Agroupofbytesforeachcommunicationiscalledapacket.

Themasterandslave(s)transferinformationviadatapackets.Thesepacketswillalwayscontainbytestostartcommunication,anaddress,alength,acommand,oneormoredataandachecksum.

Additionaloptionalvariable-lengthdatabytesoroptionalparameterscanalsobesentorreceived.Thissectionisabriefoverviewoftheprotocolspecifics.

Packet LengthJustasallwordsarenotthesamelength(numberofletters),packetsmayalsovaryinlength.Inthisprotocol,thelengthofcommandanddatafieldisputbeforecommandfieldinthepacket.Yourdatacontaining"0x42,0x41,0x44"willthenbecome“0x03,0x42,0x41,0x44”.


ChecksumDuringtransmissionofthepacket,anerrorcouldchangethevalueofthedata.Supposeinourexample,forinstance,thepacket0x03,0x42,0x41,0x44isactually0x03,0x42,0x30,0x44.Howcanyoudeterminethatthenumbersyougetarethesameasthenumberssent?

Touchpoint4serialcommunicationprotocolusesaXORcheck-characterasamethodofassigningavaluetothepackettocheckifanyofbyteshavebeenmodified.

IfallthedatabytesareXOR-edtogetherandthischeckmadeintoabyte,thisbytecouldbecalledachecksumcharacter.FortheTouchpoint4,thechecksumisthebit-wiseXORresultofallthebytesinthepacket.Inourexample,thepacketis0x03,0x42,0x41,0x44.Forthispacket,theXORresult0x44ofallthebytesaddedtothechecksummustbezero(0).Anyotherresultindicatesthereisanerrorwiththedata.

Itisusuallyimportantforthemastertothoroughlycheckdatacomingfromtheslaveforvaliditybeforeacceptingit.Thisisbecauseinmanyinstallations,analarmfromtheTouchpoint4indicatesseveredangertolifeandproperty.Themaster'sdeterminationthatanalarmexistsmaystimulateavigorousandpossiblyexpensivehumanresponse.Thereforeitisimportanttoavoidfalsealarms.Themastershouldrejectanypacketsthatcontainaninvalidstartcharacter,aninvalidaddress,aninvalidlengthbyteoraninvalidchecksum.Otherwisetheprobabilityofanevacuationbecauseofsimplenetworknoiseisunnecessarilylarge.

Theactualdatainthepacketisinterpretedinasomewhatdifferentmannerfromourpreviousexamples.BoththemasterandtheslavecommunicateusingthepacketformatinFigure 2.Itcontainsastartcode,anaddress,alength,acommandanditsassociateddata,andachecksum.Thestartcodeisfixed.Theaddressistheslaveaddressregardlessofthepacket’sorigin.Thelengthindicatesthenumberofbytesofcommandanddatafield.Thecommandindicateswhattypeofinformationisbeingtransmittedinthepacket.TheDatafieldisnullinsomecases.Ifexist,itcontainsspecificargumentsorvaluestobeinterpreted.ThechecksumisXORresultofallpreviousbytes.

ACK/NAK HandshakeEachslave(Touchpoint4)usesahandshakeschemebetweenitselfandthemaster.ThesimplestresponsebackfromtheinstrumentiscalledanACK(anabbreviationforACKnowledge).Whentheslavereceivesthehandshakecommand(0X40)packetfromthemaster,itwillsendbackanACKresponse.TheACKresponsewillbe0x01followedbythehandshakecommand0x40(see Handshake command).

Ifhowever,thechecksumdoesnotmatch,theslavewillsendaNAK(anabbreviationforNegativeAcKnowledge).ANAKindicatesthatadatapackethasbeenreceived,butthechecksumdidnotmatchwiththepacketdata.

Themastermaysendtherequestagain.AnexampleofanACKpacketis0x7F,0x01,0x02,0x40,0x01,0x3D(7FXOR01XOR02XOR40XOR01=0x3D).

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Time diagram

Figure 1. Communication time diagram

Protocol Packet Definition

Packet Format

TheformatofpacketsusingTouchpoint4SERIALCOMMUNICATIONPROTOCOLisasfollows:

Figure 2. Protocol packet format

Start Code Size:1byte.Always0x7F.

Slave Address Size:1byte. RepresentstheTouchpoint4gasdetectorcontrolleraddress, 0X01to0X10(1to16decimal).

Length Size:1byte. ThenumberofbytesintheCommandfieldandDatafield. Thetotalpacketlengthis4byteslargerthanthis.

Command Size:1byte. Thisis0x30,0x40or0x41asdefinedintheremainderofthisbook.

Data Size:0-250byte(s). Thissectionvariesaccordingtothechosencommandandmay beomitted.

Checksum Size:1byte Thebit-wiseXORresultofallthepreviousbytesinthepacket. ThismakestheXORoftheentirepacket0X00.

StartCode

SlaveAddress

Length Command Data Checksum

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Generic Data Formats

Date Format 2bytes. Bit: 1598540

Year Month Day

Figure 3. Data format

Year: (7bits) Month: (4bits) Day: (5bits)

Yearisbasedfrom1980.1989wouldbe1989-1980=9.

Time Format 2bytes

Bit: 151110540

Year Month Day

Figure 4. Time format

Hours: (5bits) Minutes: (6bits) Seconds: (5bits)

Secondsalwaysbe0.

Date/Time Examples:

Date:1F56 Oct.22.1995 Date:1F75 Nov.21,1995 Time:13C0 02:30:00 Time:7400 14:32:00 Time:4700 08:56:00

Concentration Code:

2bytes Bit: 15870

H L

Figure 5. Concentration code format

Forexample,(HEX)013Drepresentsthevalueis317.

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Concentration Data Format Code

UUXXXYYY UU Unit UU=00ppm UU=01%LEL UU=10%V/V UU=11kppm XXX reserved YYY decimalplace YYY=000 nodecimalplaces YYY=001 1decimalplace YYY=010 2decimalplaces YYY=011 3decimalplaces

Forexample,(HEX)81(10000001)represents%V/Vwith1decimalplace.

Concentration Example:

Foraconcentrationvalue(HEX)0062,98decimal,FormatCodeInterpretation:

00000000(00) 98ppm 10000001(81) 9.8%V/V 01000000(40) 98%LEL

Generic Responses

Therearefourgenericresponses.Eachoftheseresponsepacketsis6bytes,andcontainsthestartbyte,address,length,commandcode,ACK/NAKcodeandChecksum.AllACK/NAKcodeissentfollowingthecommandcodeinthelastreceivedpacket.

ACK - 0x01 Thisisusedforanacknowledgementofthehandshakecommand.

NAK - 0x21 Thisisusedforanegativeacknowledgementofpacketifthelastreceivedpackethadanincorrectchecksum.

Bad Packet - 0x66Thisissenttothemasterwhenthestartbyteorlengthinthelastreceivedpacketisincorrect.

Unknown CMD –0x67Thisresponseissentbytheslavewhenacommandisnotrecognized.

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Protocol Command Definition

Handshake command – 0x40

Thisisusedtotestforcommunicationbetweenthemasterandthespecifiedslave.

Command packet to instrument: Commandcode: 0x40 Datafield: null Checksum: 1byte

Example:Ifthemasterwantstotestthecommunicationwiththeaddressed01instrument,itshouldsendout:

0x7f0x010x010x400x3f.

Response packet from instrument: Commandcode: 0x40 ACKcode: 0x01 Checksum: 1byte

Example:Theaddressed01instrumentreceivesthehandshakecommandandresponses:

0x7f0x010x020x400x010x3d.

Get unit and points status - 0x30

Thiscommandrequeststheinstrumentdate,time,alarmstatus,faultstatusandup-to-fourchannel(s)status.

Command packet to instrument: Commandcode: 0x30 Datafield: null Checksum: 1byte

Example: 0x7f0x010x010x300x4fmeansthemasterrequeststhestatusofthe instrumentwhoseaddressis1.

Response packet from instrument: Commandcode: 0x30 Datefield: Date: 2bytes Time: 2bytes Unitalarmstatus: 1byte 0x00: noalarm 0x01: A1alarm 0x02: A2alarm 0x03: A1andA2alarm

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Unitfaultstatus: 1byte 0x00: nofault 0x01: linecircuitfault 0x02: negativedraft 0x03: inDC2ACfault 0x04: inDC2DClowvoltage 0x05: inDC2DCfault Channel(s)status: 6*nbytes (n=quantityofchannels)

Everychannelstatushas6bytes,definedasfollowing: Channelnumber: 1byte(1to4) Concentrationformat: 1byte Concentration: 2bytes Channelalarmstatus: 1byte(refertounitalarmstatus) Channelfaultstatus: 1byte(refertounitfaultstatus) Checksum: 1byte

Eachchannelstatusdatacontains6bytes,sothelengthfieldoftheresponsepacketdependsonthequantityofthechannelofTouchpoint4.Forexample,ifthereare4channels,thelengthwillbe

1(Command)+6(Data+Time+Unitalarmstatus+Unitfaultstatus)+6(bytesperchannel)*4(channels)=31.

Ifthereare2channels,thelengthwillbe

1+6+6*2=19.

NotethatonceinstrumentreceivestheGet unit and points status command,italwayssendoutallitschannels’status.

Example:

Example1: 0x7f0x010x0d0x30 0x1f0x56 date:OCT.22,1995 0x130xc0 time:02:30:00 0x01 alarm:A1alarm 0x00 fault:nofault 0x01 channelnumber:1 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0x3b checksum

TheexamplemeansthisTouchpoint4gasdetectorcontrolleronlyhasone channelconnected.

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Example2: 0x7f0x010x130x30 0x1f0x56 date:OCT.22,1995 0x130xc0 time:02:30:00 0x01 alarm:A1alarm 0x00 fault:nofault 0x02 channelnumber:2 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0x03 channelnumber:4 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0xC7 checksum

TheexamplemeansthisTouchpoint4gasdetectorcontrollerhastwo channelsconnected,Channel2andChannel4.

Example3: 0x7f0x010x1f0x30 0x1f0x56 date:OCT.22,1995 0x130xc0 time:02:30:00 0x01 alarm:A1alarm 0x00 fault:nofault 0x01 channelnumber:1 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0x02 channelnumber:2 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0x03 channelnumber:3 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0x04 channelnumber:4 0x810x000x62 concentration:9.8%V/V 0x01 alarm: A1alarm 0x00 fault: nofault 0xCE checksum

TheexamplemeansthisTouchpoint4gasdetectorcontrollerhasfour channelsconnected,Channel1toChannel4.

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Reset fault & alarm – 0x41

Thiscommandallowsaremoteresetoflatchedvisual,audioandrelayoutputsresultedfromanalarmorfault.

Command packet to instrument:Commandcode: 0x41Datafield: null

Example:Ifthemasterwantstoresetlatchedoutputsofaddressed01instrument,itshouldsendout:

0x7f0x010x010x410x3e

Response packet from instrument:Commandcode: 0x41Datafield: null

Example:Theaddressed01instrumentreceivestheresetfault&alarmcommandandresponses:

0x7f0x010x010x410x3e

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PHYSICAL LAYER

Preamble

ThephysicallayerofTouchpoint4serialcommunicationprotocolisanelectricalinterfaceinaccordancewithEIA/TIA-485standard(alsoknownasRS485standard).InTouchpoint4serialcommunicationsystem,aMasterDeviceandoneorseveralSlaveDevicescommunicateonabalancedtwistedpair,onwhichbi-directionaldataaretransmitted,atthebitrateasuserconfigured.

Electrical Interfaces

Multipoint Serial Bus InfrastructureTouchpoint4SerialCommunicationsystemimplementsa“Two-Wire”electricalinterfaceinaccordancewithEIA/TIA-485standard.Onsucha2W-bus,atanytimeonlyonedriverhastherightfortransmitting.

ThefollowingfiguregivesageneraloverviewoftheserialbusinfrastructureinTouchpoint4SerialCommunicationsystem.

Figure 6. Communication infrastructure

TheTouchpoint4gasdetectorcontrollersareconnecteddirectlytothetrunkcable.Themaster,PCorPLC,isconnecteddirectlyorviaaderivation,accordingtothemasterinstruction.Thecableshouldbeshielded.

Note:theTouchpoint4RS-485interfaceisnotelectricallyisolated.Acommonmodevoltageof7voltorgreaterbetweenanytwonodesonthenetworkwillinterferewithcommunications.ProperearthingofeveryTouchpoint4andtheMasterisessential.

Multipoint System requirementsMaximumnumberofdevices:

Althoughafigureof32devicesisalwaysauthorizedonanyRS485systemwithoutrepeater,thetotalnumberislimitedto16inTouchpoint4SerialCommunicationprotocolbecauseofaddressinglimitations.

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TopologyTouchpoint4SerialCommunicationsystemhasonetrunkcable,alongwhichdevicesareconnected,directly(daisychaining)orbyshortderivationcables.

Thetrunkcable,alsonamed“Bus”,canbelong(seehereafter).ItstwoendsshouldbeconnectedtoLineTerminations.

LengthTheend-to-endlengthofthetrunkcablemustbelimited.Themaximumlengthdependsonthebaudrate,thecable(Gauge,CapacitanceorCharacteristicImpedance),andthequantityofloadsonthedaisychain.

Foramaximum9600BaudRateandAWG26(orwider)gauge,themaximumlengthis1000m.

Ifthederivationcableisneededfortheconnectionofthemaster,thederivationmustbeshort,nevermorethan20m.

Grounding ArrangementsAtoneendofeachcableitsshieldmustbeconnectedtoprotectiveground.

Line TerminationTominimizethereflectionsfromtheendoftheRS485-cable,itisrecommendedtoplaceaLineTerminationneareachofthe2EndsoftheBus.

Itisimportantthatthelinemustbeterminatedatbothendssincethepropagationisbi-directional,butitisnotallowedtoplacemorethan2LTononepassiveD0-D1balancedpair.NeverplaceanyLTonaderivationcable.

Eachlineterminationmustbeconnectedbetweenthetwoconductorsofthebalancedline:D0andD1.

Lineterminationmaybearesistorof100ohmsto150ohms(0.5W).

Pull-up and Pull-down Resistors LinecontrolhasbeenimplementedinTouchpoint4gasdetectorcontrollersothatthebuscontainsavalid"off"signalwhennonodeistransmitting.Noexternalpull-uporpull-downresistorsareneeded.

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Mechanical Interfaces

Connectors pin-outThefollowingfigureshowsthepin-outontheterminalblockofTouchpoint4gasdetectorcontroller.

Figure 7. Touchpoint4 communication pin-out

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Issue 1 09/2007

H_MAN0847

09-07

© 2007 Honeywell Analytics 1223

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