User manual

4.4. Battery backup
The following parts of the SAM9261 Processor can be backed-up by a battery:
- the Slow Clock Oscillator;
- the Real Time Timer;
- the Reset Controller;
- the four General Purpose Backup Registers.
It is recommended to always use a backup power supply (normally a battery) in order to speed up the
boot-up time and to avoid reset problems.
4.5. Reset Controller (RSTC)
The SAM9261 has an integrated Reset Controller which samples the backup and the core voltage
(both typically at 1.2V). As the Stamp9261 uses an additional reset comparator to supervise the 3.3V
supply, the user reset function of the RSTC should always be enabled. This requires the presence of a
backup voltage (VDDBU) when the card is powered down.
4.6. Serial Number
Every Stamp9261 has a unique 48-bit hardware serial number chip which can be used by application
software. A Linux driver for reading the serial number is available.
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