SECTION SIX: Interfacing the 958 system
Page 28
958 Installation Manual, Rev. A1
Choosing the output rate
The default rate for standard NMEA 0183 output is two seconds. The 958 lets you use a one-second
update interval, a rate of 1 Hz, under limited circumstances, for NMEA and diagnostic data output.
Using the 1-Hz output option requires some thought when specifying either NMEA 0183 (NMEA
version 2.0) or Raytheon (RAY 0183). Because there isn’t enough time to transmit all available
sentences within one second, you must select for output only those that are needed. If you select
more sentences than can be output in one second, the 958 displays the following error message:
SORRY, CAN’T DO THAT. TOO MANY SENTENCES FOR 1 SEC INTERVAL
In this case, you must select fewer sentences.
There are some applications that need a longer update period. In that case, you can increase the span
to 999 seconds.
Choosing the waypoint identification (ID)
Many marine devices can display waypoint names if they’re output by the 958. At the
PORT 1 SETUP
or
PORT 2 SETUP
screen, highlight the
NMEA 0183 WAYPT ID AS
option, then press the
EDIT
menu
key. Change the option from
NUMBER
to
NAME
, and press the
ENTER
key when done. If capable, the
listening device will now display six-character waypoint names.
Choosing the checksum setting
Some older devices may not accept sentences containing the NMEA 0183 checksum that’s output by
the 958. In such cases, the device may not work properly or at all. If you have problems interfacing
to older equipment, the 958 lets you turn off the NMEA 0183 checksum: At the
PORT 1 SETUP
or
PORT 2 SETUP
screen, press the
CURSOR PAD
to highlight the
NMEA 0183 CHECKSUMS
option,
then press
EDIT
. Press the
CURSOR
PAD
to change the setting from
ON
to
OFF,
then press
ENTER
.
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
EDIT
. 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.
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.