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$PNMRX301, Ephemeris Data Transfer
This message format is used to transfer the ephemeris data between nodes, it uses a packed
hexadecimal format to transfer ephemeris data for each of the available SV’s. Since the
Ephemeris data is large and can take time to transfer over a slow serial interface, the data is
divided into individual messages for each of the SV’s. These messages are transmitted
sequentially and can be interleaved with other messages to prevent the Ephemeris data blocking
higher priority messages such as scheduled PVT information. The data for these messages is
expressed as signed or unsigned fixed point values which have been scaled from the floating point
values used in the position solution. The appropriate scaling factors are included in the table. The
ephemeris data for each satellite is divided into 3 separate messages with sequence numbers to
identify them, the contents of these frames reflects the contents of the appropriate subframes
1,2,3 transmitted from the SV’s. When transmitted these messages are generated in ascending
order of SV Id and sequence number, when being sent to the node these can be sent in any order,
provided that the 3 messages for any individual satellite are grouped together, each message is
individually interpreted and after a group of 3 valid messages for an SV the ephemeris for that SV
is updated independently. The 3 message formats are illustrated in the following tables
PNMRX301 message 1 field list
Field
Format
width scale Units
Notes
Message ID
$PNMRX301 8
PNMRX301 protocol header.
Satellite vehicle Id Int
2
Decimal satellite vehicle Id
from 1 to 32.
Subframe Id
Int
1
Subframe number 1.
Week number
Hex
3
Weeks
10 bit week number.
Health
Hex
2
6 bits.
URA
Hex
1
User range accuracy.
Time Group Delay Hex
2
2
-31
Seconds 8 bits.
IODC
Hex
3
10 bit integer.
Toc
Hex
4
2
-4
16 bits.
Af2
Hex
2
2
-31
sec/sec
2
8 bit signed integer.
Af1
Hex
4
2
-43
sec/sec
16 bit signed integer.
Af0
Hex
6
2
-31
Seconds 22 bit signed integer.
Checksum
*xx
(0) 3
2 digits.
Message
terminator
<CR> <LF>
2
ASCII 13, ASCII 10.