Filter
Top Products
60
MN002000A © 2004 Navman NZ Ltd. All rights reserved. Proprietary information and specifications subject to change without notice.
4.3.4 Differential GPS (DGPS) control
Jupiter GPS DGPS operation: disable and
correction timeout. When DGPS disable is
asserted, the navigation solution is computed
without the benefit of differential corrections even
if they are available. The DGPS timeout parameter
is used to specify the maximum allowable time
difference between current time and the validity
time of the DGPS corrections. If the timeout
is exceeded, DGPS navigation solutions are
unavailable until the correction time delta becomes
less than the timeout (see sections 4.6 and 4.7).
4.3.5 Cold start control
A simple control that enables or disables this
feature and sets the timeout for automatic
transition to cold start is available (see section 4.4
for a description of this feature).
4.3.6 Solution validity criteria
This configuration feature allows the user to
specify a set of conditions that must be met for
a navigation solution to be reported as valid.
Constraints that can be imposed on solution
validity include: use of DGPS corrections, use of
altitude, minimum number of satellites, maximum
expected position errors (EHPE and EVPE). (See
section 4.6 for a description of this feature.)
4.3.7 User-entered altitude
This configuration feature allows the user to
supply a known value of altitude that can be used
to improve the overall quality of the navigation
solution. The most common application of this
feature is to provide a mean sea level value for
a boat that is used exclusively on an ocean (see
section 4.6).
4.3.8 Vehicle platform select
This configuration feature allows the user to
specify the type of vehicle in which the Jupiter
receiver has been installed (see section 4.6).
4.3.9 Navigation control
Several navigation control features are provided by
the Jupiter GPS receivers. These features are:
• groundtrack smoothing
• position pinning
• validity criteria.
(See section 4.6 for more details.)
4.3.10 Configuration straps
Configuration straps control the use of available
configuration data at the time of initialisation.
These straps act as metacommands that can
override or complement an existing set of
configuration data.
Note: These straps are only read once at
initialisation time, so a power cycle or hardware or
software reset must be executed after any strap
changes are made.
4.3.10.1 National Marine Electronics Association
(NMEA) Select
When asserted, the host serial communication
interface is configured for NMEA operation (4800-
8-N-l). Configuration data related to the host port
that may be available from other sources is not
used. When de-asserted, operation of the host
port is controlled by any available configuration
data sources (SRAM, EEPROM, etc.). Details of
the NMEA guarantee that the receiver is started in
a known message set are contained in Section 5.0
of this document.
4.3.10.2 ROM defaults.
When asserted, all configuration and initialisation
data are obtained from ROM defaults. In addition,
SRAM is cleared to guarantee that the receiver
is started in a known operational state. The host
serial communication interface is configured for
Navman binary operation
(9600-8-N-1). When de-asserted (the normal
operational state), configuration and initialisation
data are obtained from all valid sources (SRAM,
EEPROM RTC, etc.).
4.4 Start-up modes
Jupiter GPS receivers have four types of start-up
modes (warm, initialised, cold, and frozen) based
on the availability and source of initialisation data.
Each of these modes are briefly described in the
following paragraphs.
4.4.1 Warm start
This state is present when all key data (PVT,
ephemeris, and frequency standard parameters)
is valid and available in SRAM. Two common
conditions that result in this state are a software
reset (‘hot’ start) after continuous navigation or
a return from an ‘idle’ period (power cycle) of a
few minutes that was preceded by a period of
continuous navigation.
4.4.2 Initialised start
This state is similar to warm start except that
ephemeris data is not available at start-up,
implying that SRAM was not powered during
the “idle” state or that the data time validity has
expired. Common conditions that result in this
state are user-supplied PVT initialisation or
continuous RTC operation with an accurate last
known position available from EEPROM.
4.4.3 Cold start
This state occurs as a result of unknown position
and/ or time, either of which causes an unreliable
satellite visibility list. Almanac information is