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4 OPERATING MODES
58 Copernicus GPS Receiver
18-Hour RTC Roll Over
If the Standby Mode lasts longer than 18 hours, a special condition will occur. The
real-time clock has a maximum time count of 18 hours, so that every 18 hours the
receiver must briefly power on the processor and read the elapsed time before the
real-time clock rolls over.
The Diagram below describes the Copernicus GPS Receiver current draw levels after
initiating a Standby command, as well as the service time for the 18-hour real time
clock roll over.
Figure 4.1 Current Draw Levels in Standby Mode
During the 10 msec RTC service is time, there exists a 91.6 μsec window where the
receiver cannot detect state transitions on the RX pins. If NULL characters are being
used to bring the unit out of Standby as described earlier, using three NULL
characters in a row should ensure that one of the NULL characters happens outside of
the vulnerable window so that the serial port activity is detected.
Figure 4.2 Issuing three (3) NULL Characters for Exiting Standby Mode
IMAGE TO COME
3 Null
91.6
μsec
= 70 μsec