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 DocumentMT0100P.N

©XsensTechnologiesB.V. MTiandMTxUserManualandTechnicalDocumentation

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Preamble(PRE)

Everymessagestartswiththepreamble.Thisfieldalwayscontainsthevalue250(=0xFA).

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Busidentifier(BID)orAddress

AllmessagesusedfortheMTiand  MTxusetheaddressvalue255(0xFF) indicatinga“masterdevice”. MT’s

usedontheXbushaveotherBID’s.

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MessageIdentifier(MID)

Thismessagefieldidentifiesthekindofmessage.ForacompletelistingofallpossiblemessagesseeMTiand

MTxLow‐LevelCommunicationDocument.

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Length(LEN)

SpecifiesthenumberofdatabytesintheDATAfield.Value255(=0xFF)isreserved.Thismeansthatamessage

hasamaximumpayloadof254bytes.IfLengthiszeronodatafieldexists.

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Data(DATA)

This field contains the data bytes and it has a variable length which is specified in the Length field. The

interpretationofthedatabytesaremessagespecific,i.e.dependingontheMIDvaluethemeaningofthedata

bytesisdifferent.Seethedescriptionofthespecificmessageformoredetailsaboutinterpretationofthedata

bytes.

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Checksum

Thisfieldisusedforcommunicationerror‐detection.Ifallmessagebytesexcludingthepreamblearesummed

andthelowerbytevalueoftheresultequalszero,themessageisvalidanditmaybeprocessed.Thechecksum

valueofthemessageshouldbeincludedinthesummation.

5.3.2 Messageusage

Generally, a message with a certain MID value will be replied with a message with a MID value that is

increasedbyone,i.e.theacknowledgemessage.Dependingonthetypeofmessagetheacknowledgemessage

hasnooracertainnumberofdatabytes.Insomecasesanerrormessagewillbereturned(MID=66(0x42)).

This occurs in case the previous message has invalid parameters, is not valid, or could not be successfully

executed.Anerrormessagecontainsanerrorcodeinitsdatafield.

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Example

RequestingthedeviceIDofanMTi/MTx:

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Sendingmessage:

ReqDID = 0xFA0xFF0x000x000x01(hexadecimalvalues)

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Receivingmessage(=Acknowledge):

DeviceID = 0xFA0xFF0x010x04HHHLLHLLCS(hexadecimalvalues)

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TherequestedDeviceIDisgivenintheacknowledgedmessageDeviceID(hereshownas:HHHLLHLL,the

checksum is CS). As you can see the MID (Message ID) of the acknowledgement is increased by one in

comparisonwiththesendingmessageReqDID.

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SomemessageshavethesameMIDanddependingonwhetherornotthemessagecontainsthedatafieldthe

meaningdiffers.Thisisthecasewithallthemessagesthatrefertochangeablesettings.Forexample,theMID

ofmessagerequestingtheoutputmode(ReqOutputMode)isthesameasthemessagethatsetstheoutput

mode (SetOutputMode). The difference between the two messages is that the Length field of

ReqOutputModeiszeroandnon‐zeroforSetOutputMode.