Datasheet

275
SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
16.4.6 Backup Power Supply Reset
16.4.6.1 Raising the Backup Power Supply
As soon as the backup voltage VDDUTMI rises, the RC oscillator is powered up and the zero-power power-on
reset cell maintains its output low as long as VDDUTMI has not reached its target voltage. During this time, the
Supply Controller is entirely reset. When the VDDUTMI voltage becomes valid and zero-power power-on reset
signal is released, a counter is started for 5 slow clock cycles. This is the time it takes for the 32 kHz RC oscillator
to stabilize.
After this time, the SHDN pin is asserted and the voltage regulator is enabled. The core power supply rises and the
brownout detector provides the bodcore_in signal as soon as the core voltage VDDCORE is valid. This results in
releasing the vddcore_nreset signal to the Reset Controller after the bodcore_in signal has been confirmed as
being valid for at least one slow clock cycle.
Figure 16-5. Raising the VDDUTMI Power Supply
16.4.6.2 NRSTB Asynchronous Reset Pin
The NRSTB pin is an asynchronous reset input, which acts exactly like the zero-power power-on reset cell.
As soon as NRSTB is tied to GND, the supply controller is reset generating in turn, a reset of the whole system.
When NRSTB is released, the system can start as described in Section 16.4.6.1 ”Raising the Backup Power
Supply”.
Zero-Power Power-On
Reset Cell output
22 - 42 kHz RC
Oscillator output
Fast RC
Oscillator output
Backup Power Supply
SHDN / vr_on
bodcore_in
vddcore_nreset
NRST
proc_nreset
Note: After “proc_nreset” rising, the core starts fecthing instructions from Flash at 4 MHz.
periph_nreset
7 x Slow Clock Cycles
3 x Slow Clock
Cycles
3 x Slow Clock
Cycles
6.5 x Slow Clock
Cycles
TON Voltage
Regulator
Zero-Power POR
Core Power Supply