Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

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The Supply Controller embeds a slow clock generator that is supplied with the VDDIO power supply. As soon as 

the VDDIO is supplied, both the crystal oscillator and the embedded RC oscillator are powered up, but only the 

embedded RC oscillator is enabled. This allows the slow clock to be valid in a short time (about 100 µs).
The user can select the crystal oscillator to be the source of the slow clock, as it provides a more accurate 

frequency. The command is executed by writing the Supply Controller Control register (SUPC_CR) with the 

XTALSEL bit at 1, resulting in the following sequence:

1. The PIO lines multiplexed with XIN32 and XOUT32 are configured to be driven by the oscillator. 

2. The crystal oscillator is enabled.
3. A number of slow RC oscillator clock periods is counted to cover the start-up time of the crystal oscillator 

(refer to the electrical characteristics for information on 32 kHz crystal oscillator start-up time). 

4. The slow clock is switched to the output of the crystal oscillator.
5. The RC oscillator is disabled to save power. 

The switching time may vary depending on the slow RC oscillator clock frequency range. The switch of the slow 

clock source is glitch-free. The OSCSEL bit of the Supply Controller Status register (SUPC_SR) indicates when 

the switch sequence is finished.
Coming back on the RC oscillator is only possible by shutting down the VDDIO power supply.
If the user does not need the crystal oscillator, the XIN32 and XOUT32 pins should be left unconnected. 
The user can also set the crystal oscillator in bypass mode instead of connecting a crystal. In this case, the user 

has to provide the external clock signal on XIN32. The input characteristics of the XIN32 pin are given in the 

electrical characteristics section. In order to set the bypass mode, the OSCBYPASS bit of the Supply Controller 

Mode register (SUPC_MR) must be set at 1.

The Supply Controller can be used to control the embedded voltage regulator. 
The voltage regulator automatically adapts its quiescent current depending on the required load current. More 

information can be found in the electrical characteristics section.
The user can switch off the voltage regulator, and thus put the device in backup mode, by writing SUPC_CR with 

the VROFF bit at 1.
This asserts the vddcore_nreset signal after the write resynchronization time which lasts two slow clock cycles 

(worst case). Once the vddcore_nreset signal is asserted, the processor and the peripherals are stopped one slow 

clock cycle before the core power supply shuts off.
When the user does not use the internal voltage regulator and wants to supply VDDCORE by an external supply, it 

is possible to disable the voltage regulator. This is done through ONREG bit in SUPC_MR.

The Supply Controller embeds a supply monitor located in the VDDIO power supply and which monitors VDDIO 

power supply.
The supply monitor can be used to prevent the processor from falling into an unpredictable state if the main power 

supply drops below a certain level.
The threshold of the supply monitor is programmable. It can be selected from 1.9V to 3.4V in increments of 100 

mV. This threshold is programmed in the SMTH field of the Supply Controller Supply Monitor Mode register 

(SUPC_SMMR).