Navman 12 Designer's Manual

Also see for Jupiter 12: Datasheet

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Navman 12 Designer's Manual Manual pdf 9 page image

9MN002000A © 2004 Navman NZ Ltd. All rights reserved. Proprietary information and specifications subject to change without notice.Figure 3-1 Binary message header format3.2 Binary message headerThe binary message header format has beenmodified slightly from the NavCore V format toaccommodate message logging requests. Theformat of the new message header is shown inFigure 3-1.3.2.1 Message header word 1Each input/output message starts with asynchronisation word of the form 0x81FFHEX withDEL (255 decimal) occupying the first eight bitsfollowed by the Start Of Header (SOH) (129decimal) occupying the second eight bits of thesynchronisation word.3.2.2 Message header word 2Word 2 contains the numeric message ID. Forexample, word 2 for Message ID 1000 would be:or 0x03E8 HEX .3.2.3 Message header word 3Word 3 contains the word count for the dataportion of the message. The word count does notinclude the data checksum word. A zero data wordcount indicates a ‘header-only’ message.3.2.4 Message header word 4The fourth word of the message header is a 16-bitfield allocated to protocol and message relatedflags. These flag bits extend control over ACK/NAK requests and implement message loggingrequests. The zero’s represented in the word 4field shown in Figure 3-1 are reserved bits andshould be set to zero within this word.The ACK/NAK control mechanism gives the userthe ability to request either ACK or NAK, or both,independently for each message request. The usersets the request (R) bit and either the acknowledge(A) bit or negative acknowledge (N) bit, or both, toselect the proper acknowledge behaviour. With thisapproach, the user can configure requests onlyto be NAKed, alerting the user when a problemarises without incurring the overhead necessary tocontinuously process ACKs.The lower six bits of the flags word can be usedas an additional input identifier. This identifieris not explicitly processed by the receiver; it isechoed back, in the same location, as part ofthe header in ACK/NAK responses. This featureallows the user to uniquely distinguish which inputmessage an acknowledgement corresponds towhen multiple input messages with the samemessage ID were processed during a particularperiod of time. The flags word now supportsmessage logging requests. The connect (C) anddisconnect (D) bits are used to enable and disable,respectively, message outputs, and can be usedeither independently or in conjunction with the logrequest bits.A ‘header-only’ message, with a message ID andthe connect bit set, enables the specified messagewith existing timing characteristics. Likewise, aheader-only message, with message ID and thedisconnect bit set, disables the specified message.Figure 3-2 Standard log request messageformat (data portion)A message with both connect and disconnectbits is ignored. Note that enabling and disabling amessage does not modify its timing characteristics(trigger, interval, or offset). A log request with theconnect bit set will set up the message’s timingcharacteristics and then enable the message.Similarly, for a combined log and disable request,the message will be disabled after the timingcharacteristics are set. To disable all messages,set the message ID to FFFFHEX (all bits set) and setthe disconnect (D) bit.Setting the query (Q) request bit will output themessage specified by the message ID one timeHigh Byte Low Byte0000MSB0011LSB1110MSB1000LSB