Simrad ST90 - NMEA Sentence Structure

442703/B
459
Note
Theterms"Datagram"and"telegram"aregenerallyusedtodescribethebasictransfer
unitassociatedwithapacket-switchednetwork.Inthispublication,weusetheterm
"datagram".
NMEAsentencestructure
AsentencestructureisdenedbyNMEAtoestablishthecommunicationbetweentwo
units.Mostotherdatagramformatsaredesignedusingthesame,orasimilar,structure.
Thefollowingprovidesasummaryexplanationoftheapprovedparametricsentence
structure:
$aaccc,c-c*hh<CR><LF>
1$
Thischaracter(Hex:24)isusedtoidentifythestartofasentence.
2aaccc
Thisistheaddresseld.Thersttwocharacters(aa)identifythetalkerID,while
thelastthreecharactersarethesentenceformattermnemoniccodeidentifyingthe
datatypeandthestringformatofthesuccessiveelds.
3,
Thecomma(Hex:2C)isusedasaelddelimiter.Thischaracterstartseacheld
excepttheaddressandchecksumelds.Ifitisfollowedbyanulleld,itisallthat
remainstoindicatethattherearenodataintheeld.
4c-c
Thisisthedatasentenceblock.Thisisaseriesofdataeldscontainingallthedata
tobetransmitted.Thedataeldsentenceisxedandidentiedbythesentence
formatterintheaddresseld.Dataeldsmaybeofvariablelength,andtheyare
precededbytheelddelimiter.
5*
Thischaracter(Hex:2A)isthechecksumdelimiter.Thisdelimiterfollowsthelast
eldofthesentenceandindicatesthatthefollowingtwoalphanumericalcharacters
containthechecksum.
6hh
Thisisthechecksum.
7<CR><LF>
Thecarriagereturnandlinefeedcharactersterminatethesentence.
Datagramformats