Instruction Manual

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GNAV540UserManual
7430‐0808‐01Rev.B
Page61
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Chapter8. DataPacketStructure
NOTE:ThissectionofthemanualassumesthereaderisfamiliarwithANSICprogramminglanguageanddatatype
conventions.
Theunitsupportsacommonpacketstructurethatincludesbothcommandorinputdatapackets,andmeasurement
outputorresponsepacketformats.Thissectionofthemanualexplainsthesepacketformatsaswellasthe
supportedcommands.NAV‐VIEW2.2alsofeaturesanumberoftoolsthatcanhelpauserunderstandthepacket
typesavailableandtheinformationcontainedwithinthepackets.Foranexampleofthecoderequiredtoparse
inputdatapackets,pleaseseereferto
AppendixB.SamplePacket—ParserCode.
GeneralSettings
TheserialportsettingsareRS232with1startbit,8databits,noparitybit,1stopbit,andnoflowcontrol.Standard
0,19200,38400,and57600.
baudratessupportedare:960
Common
definitionsinclude:
•
Awordisdefinedas2bytes,whichare16bits.
• Allcommunicationstoandfromtheunitarepacketsthatstartwithasinglewordalternatingbitpreamble
0x5555.ThisistheASCIIstring“UU”.
•
AllmultiplebytevaluesaretransmittedBigEndian(MostSignificantByteFirst).
• AllcommunicationpacketsendwithasinglewordCRC(2bytes).CRC’sarecalculatedonallpacketbytes
excludingthepreambleandCRCitself.InputpacketswithincorrectCRC’swillbeignored.
• EachcompletecommunicationpacketmustbetransmittedtotheGNAV540inertialsystemwithinafour(4)
secondperiod.
NumberFormats
NumberFormatConventionsinclude:
•
0xasaprefixtohexadecimalvalues
•
Singlequotes(‘’)todelimitASCIIcharacters
• Noprefixordelimiterstospecifydecimalvalues.
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Thefollowingtabledefinesnumberformats:
Table12NumberFormats
Descriptor Description Size(bytes) Comment Range
U1 UnsignedChar 1 — 0to255
U2 UnsignedShort 2 — 0to65535
U4 UnsignedInt 4 — 0to2^32‐1
I2 SignedShort 2 2’sComplement ‐2^15to2^15‐1
I2* SignedShort 2 Shifted2’sComplement Shiftedtospecifiedrange
I4 SignedInt 4 2’sComplement ‐2^31to2^31‐1