NavCom LAND-PAK Rev.N - Manual (Page 17)

Technical Reference Manual Rev. N
Blk = All; Blu = IOP w/Internal Radio ; Red = IOP & LBM ; Grn = Engine only
15
1. STX, Preamble and ETX are only used for serial communications.
2. Msg. Length is inclusive byte count from Command ID to CKSUM.
3. CKSUM is one byte XOR inclusive from Command ID through MESSAGE.
4. Messages may have a variable number of Parameters (Wx) of variable length
Message Updates & Software Revisions
From time to time it may be necessary for NavCom to change the format of an existing
message. This is normally accomplished by appending to the existing message (which will be
defined in a later version of the Technical Reference Manual). Programmers should design
software to be forward compatible by recognizing that messages may be extended and the
content of the extension may be unknown to the user. In this circumstance, the message length
will increase. Do not reject the data record if the message length and checksum are valid for
any given record. Allow the program to ignore “undefined data” to ensure forward compatibility.
NVRAM Storage
In general, when a command is stored to NVRAM, it over-writes the existing same-message in
NVRAM.
Where the output message list is concerned (NCT Proprietary, NMEA, or RTK), the receiver can
be configured to store a predetermined list using 0x20. If another output record is added using
0x20, let's say 0xEC is added to the default list (A0, AE, 44, 81, 86, B0, & B1), the message list
will be erased and contain only 0xEC unless the entire previous list is appended with EC, resent
and saved to NVRAM.
As an example, NavCom’s StarUtil program queries the message list contents from the receiver
when the appropriate window is opened. The user changes the list as desired, then StarUtil
sends the changes along with the unchanged list to over-write the existing data.