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Chapter 4 Navigation
4.1 Operating Modes
4.1.1 Continuous Tracking Mode (CTM)
CTM is the default setting of the module. While the CTM is on, the module tracks
GPS signals and estimates position continuously, i.e., satellite acquisition,
reacquisition, and tracking are the states in the CTM. This is the standard operating
mode for the general GPS receivers. Therefore, this mode is not designed for saving
power but for obtaining maximum accuracy in position. In other words, the module
with the CTM on usually operates in the Full Power State and the corresponding
operating current, which depends on the activities of CPU load, I/Os, and peripheral
hardware, may fluctuate significantly.
4.1.2 FixNOW Mode (FXN)
This is a power saving mode, which will shut down the module automatically if no
GPS signals are detectable. For further saving power consumption, the FXN allows
users to set the module into Sleep State. This mode is especially important for
power-concerned products, such as handheld devices.
During this mode, the navigation data is computed as required or at the predefined
intervals. This (navigation data) can be done by using the UBX-RXM-POSREQ or
Pin 6 “Extint 0” to wake up the module and then calculate a Position-Velocity-Time
(PVT) solution during the off-time of FixNOW Mode. The other way to wake up the
module without using serial port communication or external interrupt is to utilize the
internal RTC, which is used for a timeout setting. For enabling or disabling the FXN,
send the request by using the UBX-CFG-RXM message. For the detail configuration
of this mode, refer to the UBX-CFG-FXN message.
NOTE: The descriptions of the UBX proprietary messages are referred to Chapter 7.
NOTE: To implement the current configuration in the next time, the current one has
be saved in the Battery Backed RAM (BBR), which is powered by a backed-up battery
(1.95V ~ 3.6V), or the Flash memory.
4.2 Start-Up Modes
Table 4.1 shows the differences among cold-start, warm-start, and hot-start modes.
