Navman 11 User Manual

Page 60

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

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