# Packet Format

The units send data using an ASCII packet compatible with NMEA-0183 sentence format. All transmitter/transponder messages can be ignored (you don’t need to bother to connect the serial wires to the transmitter/transponder unless you are updating firmware). The NMEA sentence device type is "US". The message format is:

$USxxx, … \*hh

Where:

 ‘xxx’ is message type ID

… is/are variable comma-separated data fields per command

\*hh is an asterisk followed by a NMEA-compatible hex checksum

All packets end in ASCII return/linefeed (0x0D, 0x0A)

Fields within a message may be “empty” as noted in the message description, and “empty” means there is a comma for the field but no characters in the field. For example, the message below has an empty field between the fields containing “FIELD1” and the field containing “FIELD3”.

$USTXT,FIELD1,,FIELD3\*2A

Possible messages are:

$USRTH – receiver-transmitter relative angles and range

$USINF – informational message

$USERR – error message

$USDEB – developer debug message

$Gxyyy – GPS or GNSS retweeted messages, where 'x' is either 'P" or 'N'.

Beta releases may send other data formats for developer use. Some oddball messages may be provided for specific customer usage. Any message not beginning with ‘$’ may be safely ignored.


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