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

500

It can be disabled via the XTALSEL bit in the Supply Controller Control Register (SUPC_CR).

The Clock Generator integrates a 32768 Hz low-power oscillator. To use this oscillator, the XIN32 and XOUT32 

pins must be connected to a 32768 Hz crystal. Two external capacitors must be wired as shown in 

More details are given in the section “DC Characteristics” of the product datasheet.
Note that the user is not obliged to use the slow clock crystal and can use the RC oscillator instead.

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 made by writing the Supply Controller Control Register (SUPC_CR) with the 

XTALSEL bit at 1. This results in a sequence which first configures the PIO lines multiplexed with XIN32 and 

XOUT32 to be driven by the oscillator, then enables the crystal oscillator and then disables the RC oscillator to 

save power. The switch of the slow clock source is glitch free. The OSCSEL bit of the Supply Controller Status 

Register (SUPC_SR) or the OSCSEL bit of the PMC Status Register (PMC_SR) tracks the oscillator frequency 

downstream. It must be read in order to be informed when the switch sequence, initiated when a new value is 

written in the XTALSEL bit of SUPC_CR, is done.
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 can be left unconnected since by default the XIN32 and 

XOUT32 system I/O pins are in PIO input mode with pull-up after reset.
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 

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

Controller Mode Register (SUPC_MR) needs to be set at 1.
the user can set the slow clock 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 under these 

conditions are given in the product electrical characteristics section.
The programmer has to be sure to set the OSCBYPASS bit in the Supply Controller Mode Register (SUPC_MR) 

and XTALSEL bit in the Supply Controller Control Register (SUPC_CR). 

XIN32

XOUT32

GND

32768 Hz

Crystal