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9.3.2.3 Acquisition timeout
The receiver tries to obtain a position fix within the time given in the acquisition timeout. This setting is treated
as a minimum value. If the receiver determines that it needs more time for the given starting conditions, it will
automatically prolong this time. If set to zero, the acquisition timeout is exclusively determined by the receiver.
In case of a very weak or no GPS signal, the timeout determined by the receiver may be shortened in order to
save power. However, the acquisition timeout will never be shorter than the configured value.
9.3.2.4 On time and wait for timefix
The on time specifies how long the receiver stays in Tracking state before switching to POT and Inactive for
update state respectively. The quality of the position fixes can be configured by setting the masks in the
message UBX-CFG-NAV5. If the wait for timefix option is enabled the transition from Acquisition to Tracking
state is made only if the time is known and within the configured limits, and the receiver is continuously
producing position fixes for more than two seconds. Thus enabling the wait for timefix option usually delays
the transition from Acquisition to Tracking state by a few seconds. Keep in mind that setting harder limits in
UBX-CFG-NAVX5 will prolong start-up time so you might want to increase the acquisition timeout.
9.3.2.5 Do not enter 'inactive for search' state when no fix
If this option is enabled, the receiver acts differently in case it can't get a fix: instead of entering Inactive for
search state, it keeps trying to acquire a fix. In other words, the receiver will never be in Inactive for search state
and therefore the search period and the acquisition timeout are obsolete.
9.3.2.6 Update RTC and Eph
To maintain the ability of a fast start-up, the receiver needs to calibrate its RTC and update its ephemeris data
on a regular basis. This can be ensured by activating the update RTC and update Eph option. The RTC is
calibrated every 5 minutes and the ephemeris data is updated approximately every 30 minutes. See chapter
Satellite data download for more information.
9.3.2.7 EXTINT pin control
The pin control feature allows overriding the automatic active/inactive cycle of Power Save Mode. The state of
the receiver can be controlled through either the EXTINT0 or the EXTINT1 pin.
If the Force-ON feature is enabled, the receiver will not enter the Inactive states as long as the configured
EXTINT pin (either EXTINT0 or EXTINT1) is at a 'high' level. The receiver will therefore always be in Acquisition/Tr
acking states (ON/OFF operation) and Acquisition/Tracking/POT states (cyclic tracking operation) respectively.
When the pin level changes to 'low' the receiver continues with its configured behavior. UBX-CFG-PM2 is used
to select and configure the pin that will control the behavior as described above.
If the Force-OFF feature is enabled, the receiver will enter Inactive state (with a delay of up to five seconds) and
remain there until the next wake-up event. Any wake-up event can wake up the receiver, even while the
EXTINT pin is set to Force-OFF. However, the receiver will only wake up for the time period needed to read the
configuration pin settings, i.e. Force-OFF, and will then enter Inactive state again.
9.3.2.8 Grid offset
Once the receiver has a valid time, the update grid is aligned to the start of the GPS week (Sunday at 00:00
o'clock). Before having a valid time, the update grid is unaligned. A grid offset now shifts the update grid with
respect to the start of the GPS week. An example of usage can be found in chapter Use grid offset.
The grid offset does not work in cyclic tracking operation.
GPS.G6-SW-10018-A Public Release Page 22 of 201