Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Data Sheet
Product codes
ATSAM4E-XPRO
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
574
29.4.2 Slow Clock Crystal Oscillator
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
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.
Figure 29-2.
Typical Slow Clock Crystal Oscillator Connection
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 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.
frequency. The command is made by writing 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.
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.
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.
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 SUPC_MR and XTALSEL bit in SUPC_CR.
XIN32
XOUT32
GND
32768 Hz
Crystal