Motorola M12 Oncore User's Guide download pdf (Page 116)

Chapter 5 - I/O Commands

ALMANAC DATA REQUEST (@@Be)

Applicability: M12+ Timing and Positioning Receivers

This command is used to command the M12+ to output its current almanac data. The user has

the option of requesting the almanac data output one time (polled), or each time the almanac data

changes (continuously).

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 M12+ 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 @@Cb prefix and the checksum, carriage return,

and line feed for each output. The output message begins with subframe 5 page 1.

The M12+ 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 receiver does not contain an almanac, the receiver

returns one response message with the subframe and page bytes equal to zero.

Default mode: Polled

Legacy Code Compatibility: The @@Be command was implemented in an identical fashion on

virtually all Motorola Oncore receivers.

Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05

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Motorola M12 Oncore User's Guide Page 116