406273/C
489
ElectronicDevicesdocumentexplainstheformatsindetail.Thedocumentcanbe
obtainedfromNMEA.
Note
Theterms"Datagram"and"telegram"aregenerallyusedtodescribethebasictransfer
unitassociatedwithapacket-switchednetwork.Inthispublication,weusetheterm
"datagram".
NMEAsentencestructure
Asentencestructureisdeîš¿nedbyNMEAtoestablishthecommunicationbetweentwo
units.Mostotherdatagramformatsaredesignedusingthesame,orasimilar,structure.
Thefollowingprovidesasummaryexplanationoftheapprovedparametricsentence
structure:
$aaccc,c-c*hh<CR><LF>
1$
Thischaracter(Hex:24)isusedtoidentifythestartofasentence.
2aaccc
Thisistheaddressîš¿eld.Theîš¿rsttwocharacters(aa)identifythetalkerID,while
thelastthreecharactersarethesentenceformattermnemoniccodeidentifyingthe
datatypeandthestringformatofthesuccessiveîš¿elds.
3,
Thecomma(Hex:2C)isusedasaîš¿elddelimiter.Thischaracterstartseachîš¿eld
excepttheaddressandchecksumîš¿elds.Ifitisfollowedbyanullîš¿eld,itisallthat
remainstoindicatethattherearenodataintheîš¿eld.
4c-c
Thisisthedatasentenceblock.Thisisaseriesofdataîš¿eldscontainingallthedata
tobetransmitted.Thedataîš¿eldsentenceisîš¿xedandidentiîš¿edbythesentence
formatterintheaddressîš¿eld.Dataîš¿eldsmaybeofvariablelength,andtheyare
precededbytheîš¿elddelimiter.
5*
Thischaracter(Hex:2A)isthechecksumdelimiter.Thisdelimiterfollowsthelast
îš¿eldofthesentenceandindicatesthatthefollowingtwoalphanumericalcharacters
containthechecksum.
6hh
Thisisthechecksum.
7<CR><LF>
Thecarriagereturnandlinefeedcharactersterminatethesentence.
Datagramformats
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