DR + GPS
STARTER KIT REFERENCE MANUAL
Lassen DR + GPS Reference Manual 101
Initialization Information
The following reports contain the information that the module is currently storing
in BBRAM for initialization in the next session. If any information is updated in
real time through data decode or fixes the module reports the updated
information.
When these reports are used with the “set” command, the host sends the
message with the “Source” byte set to “Host Input”. If the information is already in
use in the system and validated by fixes or decode, the module may reject the
host input. This will be indicated in the acknowledgment message. Validated data
can be over-written using the “Host override” option.
If BBRAM is lost, byte 3 of the start-up message 12-01 will indicate the module is
doing a cold-start. The host can upload the initialization information to the module
using the set procedure to speed GPS satellite acquisition. This information
includes:
1. Almanac messages (28-12, 28-13, 28-14);
2. Time message (29-01);
3. Frequency message (29-04); and
4. Latitude / longitude message (29-02).
Of the above list, the frequency message is optional but the others are required
for “warm-start” performance. The order of data entry is important. The latitude /
longitude message 29-02 must be provided after the time, almanac, and
(optionally) frequency messages, because this message triggers an immediate
satellite re-selection using the new data. The other initialization messages
(altitude, DR calibration, ephemeris) will also speed the first fix, and can be sent
either before or after the latitude / longitude message.
Many of the data structures in this section have “source” and “newness” fields. A
set command can use values 0 (clear), 1 (host input), or 2 (host override) for the
source field. If the source is currently 2 (host override) or 3 (derived from GPS)
and a new set command has source value 1 (host input), the acknowledgment
message returns error “value contradict” for set command. The newness field
cannot be set; if newness is 0, a reset has occurred since the value was last
updated.