Motorola M12 Oncore User Manual page 46

Motorola GPS Products
M12 Oncore User' s Guide Supplement
Revision 1.0 01/25/00
ALMANAC DATA OUTPUT
This command is used to output the almanac data. The user has the option of
requesting the almanac data output one time (polled), or each time the almanac data
changes (continuously).
The state of the mode parameter is stored in RAM. If the GPS receiver was
continuously outputting the almanac data when turned off, and backup power is
applied, then it will begin to output this message continuously again when the main
power is reapplied. If backup power is not applied during power down, then the
GPS receiver will start up in polled only mode.
Almanac data for the GPS satellites is transmitted in words 3 through 10 of
subframe 5 (pages 1 through 25), and words 3 through 10 of subframe 4 (pages 2
through 5, 7 through 10, and 25) of the satellite broadcast data message. Refer to
the ICD-GPS-200 for a detailed almanac data description.
The GPS receiver outputs the almanac data through a series of output messages,
each of which is identified by the particular subframe and page numbers. The data
fields of each individual message correspond to words 3 through 10 of the broadcast
data. Each word contains 24 data bits.
The entire almanac data output consists of 34 output response messages
corresponding to the 25 pages of subframe 5 and the 9 pages in subframe 4 that
contain almanac data (pages 2 through 5, 7 through 10, and 25). The total message
output for one output request is 1122 bytes including the @@Be prefix and the
checksum, carriage return, and line feed for each output. The output message
begins with subframe 5 page 1.
The GPS receiver will output about 750 bytes of message data for each one second
output opportunity. If selected, the almanac response message is output until the
total number of bytes sent in a one-second epoch exceeds 750. The remainder of the
almanac message is sent in the next one-second epoch (up to the 750 byte limit per
second) until all of the almanac data is output.
If the user issues this command and the GPS receiver does not contain an almanac,
then the GPS receiver returns one response message with the subframe and page
bytes equal to zero.
Default mode: Polled
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