Manual

June 2004 Isis® Sonar User's Manual, Volume 2
52
D.4.1.1 How Isis Deals With Heading Issues in NMEA0183
Strings
Isis can process heading packets that can occur in NMEA0183 strings. Two
packets in particular affect the behavior of Isis:
HEHDT
HCHDT
When both are being received, HEHDT takes priority over HCHDT.
D.4.1.2 How Isis Deals With Time Issues in NMEA0183
Strings
Isis can be synchronized or de-synchronized with the computer clock with
respect to NMEA0183 strings. Syncing the Isis computer clock is now
determined by taking the time from a single packet type. The priority is:
NMEA_ZDA 4 // This is most preferable.
NMEA_RMC 3
NMEA_GLL 2
NMEA_GGA 1 // This is least preferable.
NMEA_ANY 0
NOCLOCK // This prevents Isis from synchronizing Isis system
clock with GPS time. By default, Isis always synchronizes the
system clock with GPS time.
Some parts of the NMEA0183 template are not affected by the NO modifier.
Additional tokens after NMEA0183 further control the processing of NMEA
packets:
POS=NODIFF //This causes Isis to use only non-differential
positions from GGA packets.
POS=DIF //This causes Isis to use only differential positions
from GGA packets.
NOCLOCK //This prevents Isis from synchronizing Isis system
clock with GPS time. By default, Isis always
synchronizes the system clock with GPS time.
UTM //This forces nav as UTM (meters). By default, when
NMEA0183 is selected as a template, navigation is
Appendix D: Serial Interfaces