NMEA TLL datagram format
The NMEA TLL datagram contains target information; number, name, position and time tag. The TLL datagram allows the sonar system to receive information about targets that are tracked by other systems.
Format
$--TLL,xx,llll.ll,a,yyyyy.yy,a,c--c,hhmmss.ss,a,b*hh <CR><LF>
Description
1 $—Talker identifier
2 TLLDatagram identifier
3 xxTarget number
4 llll.ll,aTarget latitude
•  N = North
•  S = South
5 yyyyy.yy,aTarget longitude
•  E = East
•  W = West
6 c--cTarget name
7 hhmmss.ssCoordinated Universal Time (UTC)
8 aTarget status
•  L = Lost
•  Q = Query
•  T = Tracking
9 bValue is set to "R" if target is a reference used to determined own-ship position or velocity.
10 *hh: Checksum