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SECTION SIX: Interfacing the 958 system
958 Installation Manual, Rev. A1 Page 27
If you want to set all the sentences to the factory settings for recommended output, press the SAFE
RESET menu key. If you want to turn on only a select few sentences for output, press the ALL OFF
menu key to turn off all sentences, then turn the desired ones back on.
Choosing the talker ID
The NMEA 0183 standard requires that the equipment you’re interfaced to—the “listener”—knows
what type of device is transmitting the data. The 958’s talker ID tells the listener that it is receiving
information from a navigation source, not a communications or sensor device—which transmits
completely different forms of data. Certain listening devices will only accept navigation data
identified as coming from loran (LC), GPS (GP), or an integrated instrument (II). The 958 lets you set
its talker ID to LC, GP, or II to match what the listener device is expecting:
1. Check the listener device’s instruction manual to determine which “talker ID”
codes it will respond to.
2. At the PORT 1 SETUP or PORT 2 SETUP screen, press the CURSOR PAD to
highlight the NMEA 0183 TALKER ID option, then press the EDIT menu key.
3. Scroll through the three choices using the CURSOR PAD to make your selection,
and press the ENTER key. The interfaced equipment will now receive the 0183
data in the correct nav-source format.
Choosing the lat/lon precision
For more flexibility when communicating with a variety of other devices, you can set the precision
level of the 0183 position information output by the 958. The choice you make depends on the
equipment to which you’re outputting the NMEA data (for the number of digits of precision required
for that particular device, see the manufacturer’s instructions). You have three choices:
• XX.XX ’ (lat/lon precision to two decimal places/hundredths of minutes/or 60 feet)
• XX.XXX ’ (lat/lon precision to three decimal places/thousandths of minutes/or 6
feet; this is the factory setting)
• XX.XXXX ’ (lat/lon precision to four decimal places/ten-thousands of minutes/or
roughly ½ foot)
The 958 conforms to the NMEA version 2.00 standard, and is also compatible with version 1.50.
Electronic and pen plotting devices typically benefit the most from three and four decimal places of
precision. However, many older devices (and some current autopilots) designed to operate with the
original 0183 and other formats can only function with two-place precision.
NOTE:
Position information can be output and displayed to four
decimal places, but the ability to actually navigate with such
accuracy is limited by the accuracy of the Loran and GPS
systems. Therefore, choosing more decimal places doesn’t
necessarily increase navigating accuracy.