Manual

June 2004 Isis® Sonar User's Manual, Volume 2
55
D.4.2 Disabling ASCII Reports Produced by NMEA
Packets
Some GPS (or Loran) receivers will produce, by default, copious ASCII
reports in addition to the standard NMEA0183 packets over the serial
interface. These reports can contain receiver diagnostic information, satellite
position, and other similar data items. The sheer size of these reports can
overload the Isis input buffer and cause the system to work unnecessarily
hard as it tries to parse the reports.
Completely disable the GPS ASCII reporting mechanism before
using Isis.
In most cases, you can disable the ASCII reports by working through the
menus on the front of the GPS receiver. You only want the standard
NMEA0183 data packets to go through the serial interface: $GPGLL,
$GPGGA, $GPZDA, etc. With the ASCII reporting mechanism disabled, Isis
will ignore all $GPxxx messages that Isis doesn’t specifically parse.
To verify from Isis that ASCII reports aren’t being sent by the GPS receiver,
use the Test button in the Serial Port Setup dialog box to monitor the serial
data. You can also monitor serial data from the com Port Test submenu
found in the Tools menu.
D.5 Special Serial Receive Strings
Except when using NMEA0183 functions, some strings, when received over any
active serial port, cause Isis to perform special internal functions (Table D-1).
Appendix D: Serial Interfaces