GPS-RECEIVER JP7-T
VERSION 1.02
6.3.2 Warm
start
This start-up procedure so called Warm start is performed when the time
and position are known to within some limits, as well the almanac data are
known and at least 3 Satellites Ephemeris are valid from previous operation.
The validity of this data is dedicated if the receiver is switched off for more
than 2 hours. If the receiver has been moved for more than 100 miles or the
accurate time is currently not available then the Ephemeris data can be
invalid. In such case the receiver will have to acquire the satellites and to
collect the Ephemeris data which are in this scenario required.
6.3.3 Hot
start
This start-up procedure so called Hot start is performed when the time and
position are accurate known, as well the almanac data are also valid. The
validity of this data is dedicated if the receiver has been switched off for less
than 2 hours and the real-time clock (RTC) has been operating during that
switch off time. This start-up procedure performs computing of valid
positions, only.
The problems which may be met while start-up modes:
The validity of the Real-time Clock (RTC) during start-up is determined in
part through a checksum of the SRAM to see if it has been corrupted. If the
SRAM checksum shows the memory has been corrupted, the RTC is also
assumed to be invalid and the system ignores the RTC value. In this case,
the system will not perform a hot start, but will fall back to a cold start mode
with a longer time to first fix (TTFF), on the order of less than 45 seconds
typical. These problems may happens in case of the RTC randomly drop
counts under minimal supply voltage conditions which is supplied from
external connected backup battery and supports the RTC operation (+3.0
VDC –5%).
6.4 Product
applications
-
Handheld GPS receiver applications
- Automotive
applications
-
Marine navigation applications
- Aviation
applications
-
Timing applications
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