Kantronics KAM 98, Руководство пользователя

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+ In some applications, you may wish to keep your PC or terminal attached to the
TNC for packet operations, yet switch serial port connection to the GPS unit peri-
odically — just to update your location. This arrangement is handy when only
one COM port is available on your PC. This can be accomplished with a
Kantronics APRS-HSP cable.
Cabling a GPS Unit to a Kantronics TNC
The NMEA standard specifies that the signals in the GPS receiver data port fol-
low the EIA-422 standard.
Technical note: Many GPS vendors simply use “TTL” voltage levels (+5 volts and
0 volts), but use the same polarity as RS-232. These units are capable of driving a
Kantronics TNC RS-232 serial data port input pin. However, some GPS vendors in-
vert the sense of this signal (true TTL), and these units will not directly interface
with a TNC.
Warning: The Kantronics TNC serial ports are RS-232; that is, they provide for
signals that swing plus and minus approximately 8 volts. Check your GPS manual
before connecting this port to your GPS device to make sure that it is capable of
handling these voltages. Kantronics is not responsible for damage wherein its
TNCs are attached to other devices; see the Kantronics Limited Warranty.
To connect the data port of a GPS unit to your TNC, you’ll need a three-wire ca-
ble. A shielded cable is preferred. Refer to your GPS manual to determine which
pins are used for signal ground, data output to an RS-232 device, and data input
from an RS-232 device (such as the TNC). At least two of these wires must be
connected at both ends of the cable:
•
connect the signal ground wire of the GPS data port to pin 7 of the TNC
serial port. This wire may be identified as “NMEA-” by some GPS
vendors.
•
connect the “data output pin” of the GPS data port to pin 2 of the TNC
serial port. The data output pin may be identified as “NMEA+” by some
GPS NMEA Interfacing Capability Packet Modes of Operation
KAM’98 v 8.3 181 User’s Guide