Owner's manual
440UserM
7430‐0131‐01Rev.F
NAV anual Page61
PayloadLength
Thepayloadlengthisalwaysaonebyteunsignedcharacterwitharangeof0‐255.Thepayloadlengthbyteisthe
length(inbytes)ofthe<variable length payload>portionofthepacketONLY,anddoesnotincludetheCRC.
Payload
Thepayloadisofvariablelengthbasedonthepackettype.
16‐BitCRC‐CCITT
Packetsendwitha16‐bitCRC‐CCITTcalculatedontheentirepacketexcludingthe0x5555headerandtheCRCfield
itself.Adiscussionofthe16‐bitCRC‐CCITTandsamplecodeforimplementingthecomputationoftheCRCis
includedattheendofthisdocument.This16‐bitCRCstandardismaintainedbytheInternational
Union(ITU).
Telecommunication
Width:16bits
Polynomial:0x1021
Initialvalue:0xFFFF
ORisperforme
NoX donthefinalvalue.
Referto
AppendixC.SamplePacket—ParserCodeforsamplecodethatimplementsthe16‐bitCRCalgorithm.
MessagingOverview
Thefollowingtablesummarizesthemessagesavailablewitha440Seriesmodel.Packettypesareassignedmostly
usingtheASCIImnemonicsdefinedaboveandareindicatedinthesummarytablebelowandinthedetailedsections
foreachcommand.Thepayloadbyte‐lengthisoftenrelatedtootherdataelementsinthepacketasdefinedinthe
tablebelow.Thereferencedvariablesaredefinedinthefollowingsections.
Outputmessagesaresentfromthe440Seriesinertialsystemtotheusersystemasaresultofapollrequestora
continuouspacketoutputsetting.Inputmessagesaresentfromtheusersystemtothe440Seriesinertialsystem
andwillresultinanassociatedReplyMessageorNAKmessage.Replymessagestypicallyhavethesame
<2byte
ackettype(U2)>
p
astheinputmessagethatevokeditbutwithadifferentpayload.
Table13MessageTable
ASCII
Mnemonic
<2‐bytepacket
ype(U2)>
t
<payload
byte‐length
U1)>
(
Description Type
Available
unctions
F
LinkTest
PK 0x504B 0
PingCommand
andResponse
Input/ReplyMessage ALL
CH 0x4348 N
EchoCommand
andResponse
Input/ReplyMessage ALL
InteractiveCo mmands
GP 0x4750 2
GetPacket
Request
InputMessage ALL
AR 0x4152 0 AlgorithmReset Input/ReplyMessage VG,AHRS,NAV