When the TNC resets (either from a RESET command or by turning the TNC off
and then on) it will be in the GPS Mode, and the GPSINIT string (if any) will be
sent to the serial port.
Normally, you would set the INTFACE command to GPS, turn the TNC off, con
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nect your GPS unit, and then turn the GPS unit ON and then turn the TNC ON.
When operating in the GPS Mode, the TNC will automatically update the LT
buffers every time it receives the designated NMEA strings from the GPS re
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ceiver.
Exiting GPS Mode
If you want to exit the GPS Mode (perhaps to set new parameters), connect your
computer or terminal to the serial port of the TNC and type three <Ctrl+C> char-
acters. The TNC will reset and the INTFACE command will be set to TERMI-
NAL.
+ Hint: You may have changed the ABAUD setting (usually to 4800) for the GPS
mode. If so, before you can use the three <Ctrl+C> characters to exit GPS mode,
you must set your RS232 baud rate in your computer to the same as the ABAUD
setting in your TNC.
Other GPS Features
Slotted Beacons
The BLT command provides for the ability to specify not only the interval be
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tween beacons, but a starting time for the beacons. This permits a “slotted” sys
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tem of beacons by numerous stations. For instance, lets say your local area has 30
stations that each should beacon their location every 30 minutes. A beacon would
be transmitted every n minutes from the time the user sets the time that the bea
-
con should be transmitted. As an example, if you set the BLT command for LT 1
(BLT 1) with the command:
BLT 1 EVERY 00:30:00 START 00:00:01
the TNC would transmit a beacon at 00:00:01 (time after midnight) and every 30
minutes after that.
The second user could set the BLT with the command:
BLT 1 EVERY 00:30:00 START 00:01:01
GPS NMEA Interfacing Capability Packet Modes of Operation
KAM’98 v 8.3 185 User’s Guide
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