Power-Up; Power-On Reset And Brown-Out Detector - Atmel SAM L22G Manual

8.3.

Power-Up

This section summarizes the power-up sequence of the SAM L22. The behavior after power-up is
controlled by the Power Manager.
Related Links
PM – Power Manager
8.3.1. Starting of Internal Regulator
After power-up, the device is set to its initial state and kept in Reset, until the power has stabilized
throughout the device. The default performance level after power-up is PL0.
The internal regulator provides the internal VDDCORE corresponding to this performance level. Once the
external voltage VDDIO and the internal VDDCORE reach a stable value, the internal Reset is released.
Related Links
PM – Power Manager
8.3.2. Starting of Clocks
Once the power has stabilized and the internal Reset is released, the device will use a 4MHz clock by
default. The clock source for this clock signal is OSC16M, which is enabled and configured at 4MHz after
a reset by default. This is also the default time base for Generic Clock Generator 0. In turn, Generator 0
provides the main clock GCLK_MAIN which is used by the Power Manager (PM).
Some synchronous system clocks are active after Start-Up, allowing software execution. Refer to the
"Clock Mask Register" section in the PM-Power Manager documentation for the list of clocks that are
running by default. Synchronous system clocks that are running receive the 4MHz clock from Generic
Clock Generator 0. Other generic clocks are disabled.
Related Links
PM – Power Manager
8.3.3. I/O Pins
After power-up, the I/O pins are tri-stated except PA30, which is pull-up enabled and configured as input.
8.3.4. Fetching of Initial Instructions
After Reset has been released, the CPU starts fetching PC and SP values from the Reset address,
0x00000000. This points to the first executable address in the internal Flash memory. The code read from
the internal Flash can be used to configure the clock system and clock sources. See the related
peripheral documentation for details. Refer to the ARM Architecture Reference Manual for more
information on CPU startup (http://www.arm.com).
Related Links
PM – Power Manager
GCLK - Generic Clock Controller
OSCCTRL – Oscillators Controller
OSC32KCTRL – 32KHz Oscillators Controller
8.4.

Power-On Reset and Brown-Out Detector

The SAM L22 embeds three features to monitor, warn and/or reset the device:
• POR: Power-on Reset on VSWOUT and VDDIO
on page 188
on page 188
on page 188
on page 188
on page 121
on page 207
on page 258
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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