Instruction Manual

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Page62
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GNAV540UserManual
7430‐0808‐01Rev.B
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Descriptor Description Size(bytes) Comment Range
F4 FloatingPoint 4
IEEE754Single
ion
Precis
‐1*2^127to2^127
SN String N ASCII 
PacketFormat
lloftheInputandOutputpackets,exceptthePingcommand,conformtothefollowingstructure:A
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0x5555 <2‐bytepackettype(U2)> <payloadbyte‐length(U1)> <variablelengthpayload> <2‐byteCRC(U2)>
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ThePingCommanddoesnotrequireaCRC,soaGNAV540unitcanbepingedfromaterminalemulator.ToPinga
GNAV540unit,typetheASCIIstring‘UUPK’.Ifproperlyconnected,theGNAV540unitwillrespondwith‘PK’.All
otherc
ommunicationswiththeGNAV540unitrequirethe2‐byteCRC.
NOTE:AGNAV540unitwillalsorespondtoapingcommandusingthefullpacketformationwithpayload0and
correctlycalculatedCRC.Example:0x5555504B009ef4.
PacketHeader
Thepacketheaderisalwaysthebitpattern0x5555.
PacketType
Thepackettypeisalwaystwobyteslonginunsignedshortintegerformat.Mostinputandoutputpackettypescan
beinterpretedasapairofASCIIcharacters.Asasemanticaidconsiderthefollowingsinglecharacteracronyms:
Table13CharacterAcronyms
AcronymDescription
P Packet
F Fields:ReferstoFieldswhicharesettingsordatacontainedintheunit
E EEPROMReferstofactorydatastoredinEEPROM
R Read:Readsdefaultnon‐volatilefields
G Get:Ge scurrentvolatilefieldsorsettingst
W
Write: Writesdefaultnon‐volatilefields.Thesefieldsarestoredinnon‐volatilememoryand
determinetheunit’sbehavioronpowerup.Modifyingdefaultfieldstakeeffectonthenextpower
upandthereafter.
S
Set:Setscurrentvolatilefieldsorsettings.Modifyingcurrentfieldswilltakeeffectimmediatelyby
modifyinginternalRAMandarelostonapowercycle.
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