User`s guide

Chapter 5 - I/O Commands
ALMANAC DATA INPUT (@@Cb)
Applicability: M12+ Timing and Positioning Receivers
This command allows the user to load a previously recorded almanac into the M12+'s RAM via
the serial port. The entire almanac data message consists of 34 unique formatted messages that
correspond to the subframe and page number of the almanac data (see GPS-ICD-200 for format
description).
It is not necessary to input an almanac at power up. If backup power has been applied, the
almanac will be retained in RAM. If the almanac is not available, it will be downloaded from the
satellites. This can take anywhere from 15 to 30 minutes if satellites are tracked continuously.
Manually loading an almanac using this command will reduce the TTFF.
The receiver echoes the input almanac data subframe and page numbers of messages received
so the user can validate that each almanac slice has been accepted. It is not necessary nor is it
recommended to wait for an echo before sending the next data page. The M12+ receiver will
collect an entire almanac in local storage, then check the almanac for validity. The receiver will
update the internal almanac data with the new user-supplied almanac upon completion of the
receipt of a valid almanac.
Any single input message that has an invalid subframe (i.e., not 4 or 5) will reset the almanac
collection software so that the local collection of almanac data can begin fresh. Subframe 5, Page
1 marks the beginning message and resets the collection process. The data for Subframe 5,
Page 1 must appear first in the string of 34 commands that make up the total almanac input data.
The order for the remaining data is not important.
The user can insert up to about 1K of data per second into the serial port. Consequently, the user
should be aware that the 34 total messages (of 33 bytes each) that make up the almanac data
will take longer than one second to input into the receiver.
Legacy Compatibility: The @@Cb message was used in an identical manner in virtually all earlier
Motorola receivers.
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
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