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SECTION SIX: Interfacing the 957 system
Page 46 957 INSTALLATION MANUAL, Revision C1
Choosing the checksum
setting
Some older devices may not accept sentences containing the
NMEA 0183 checksum that’s output by the 957. In such cases,
the device may not work properly or at all. If you have
problems interfacing to older equipment, the 957 offers the
flexibility to turn off the NMEA 0183 checksum:
1. At the PORT 1 SETUP or PORT 2 SETUP screen, press the
CURSOR PAD to highlight the NMEA 0183 CHECKSUMS
option, then press the EDIT menu key.
2. Press the CURSOR PAD to change the setting from ON to
OFF, and press the ENTER key when done.
Selecting an independent
NMEA output-port datum
You can adjust the geodetic datum for NMEA 0183 ports 1 and
2, separately from the datum you choose for position display. At
the PORT SETUP 1 or PORT SETUP 2 screen, highlight the
OUTPUT DATUM option, then press the EDIT menu key. Scroll
through the choices to make your selection. To apply this
chosen datum to the lat/lon coordinates in the NMEA 0183
output sentences, press the ENTER key.
Using 200 ppnm
output
The 957 provides an open-collector transistor output (on pin
14) that’s programmed to produce 200 pulses per nautical mile.
The emitter of the NPN transistor is connected to ground, and
its collector connects to the output pin (see Figure 16: ”Wiring
for 200 PPNM output,” below). The output can sink 100mA,
and can withstand a maximum positive voltage of 50 volts.If
the output connects to an inductive device (for example, a
NOTE:
Be sure to see if the listening device can do this
before you change the
NMEA WAYPT ID AS
option. Many older devices won’t understand this
identifier, and using it may cause problems with
displaying waypoint information or when following
routes.
There is no standard for identifying how numbers
should be assigned when converting waypoints
from names to numbers. When you export
waypoint information as numbers to a peripheral
device, be aware that numbers aren’t sequentially
defined and may be re-used on a random basis.