User Manual
Table Of Contents
- Document History
- Introduction
- Product Concept
- GSM Application Interface
- GSM/GPRS Operating Modes
- Power Supply
- Power Up / Down Scenarios
- Automatic GPRS Multislot Class Change
- Charging Control of the GSM Part
- Power Saving
- Summary of State Transitions (Except SLEEP Mode)
- RTC Backup for GSM Part of XT55/56
- Serial Interfaces of the XT55/56 GSM Part
- Audio Interfaces
- SIM Interface
- Control Signals
- GPS Application Interface
- GSM and GPS Antenna Interfaces
- Electrical, Reliability and Radio Characteristics
- Mechanics
- Reference Approval
- Example Applications
- List of Parts and Accessories
XT55/56 Hardware Interface Description
Confidential / Preliminary
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XT55/56_hd_v02.96 Page 80 of 125 18.08.2005
4.10 Start-up Procedures
The start-up strategy of the XT55/56 GPS part depends on the last position, current time and
ephemeris data, that the receiver has stored the external SRAM memory. There are three
different start-up procedures:
4.10.1 Coldstart
The coldstart takes place when the receiver has no knowledge of its last position or time. In
this case the GPS RTC has not been running and no valid ephemeris data or almanac data
is available (The receiver has never been navigating or no battery backup memory
available).
4.10.2 Warmstart
This start-up procedure is performed whenever the receiver is able to use the valid almanac
data, and has not in an important manner moved since the last valid position calculation. This
procedure starts if the receiver has been shut off for more than 2 hours, but the last position,
time and almanac are still acknowledged. This procedure is able to announce the current
visible satellites in advance. However, since ephemeris data are not available or cannot
longer be used, the receiver has to wait for the ephemeris broadcast to complete.
4.10.3 Hotstart
Hotstart is performed whenever the receiver still has access to valid ephemeris data and
exact time. This procedure starts if the receiver has been shut off for less than 2 hours and
the GPS RTC has been running during that time. Furthermore, during the previous session,
the receiver must have been navigating (to allow it to decode and store ephemeris data).
In Hotstart, the receiver can announce in advance the currently visible satellites, and is
therefore able to quickly obtain and track the signal. Due to the fact that ephemeris is already
known, there is no need to wait for the ephemeris broadcast to complete.