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ATSAM4S-XPLD
242
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
14.4
Functional Description
14.4.1 Reset Controller Overview
The Reset Controller is made up of an NRST Manager and a Reset State Manager. It runs at Slow Clock and generates
the following reset signals:
the following reset signals:
proc_nreset: Processor reset line. It also resets the Watchdog Timer
periph_nreset: Affects the whole set of embedded peripherals
nrst_out: Drives the NRST pin
These reset signals are asserted by the Reset Controller, either on external events or on software action. The Reset
State Manager controls the generation of reset signals and provides a signal to the NRST Manager when an assertion of
the NRST pin is required.
State Manager controls the generation of reset signals and provides a signal to the NRST Manager when an assertion of
the NRST pin is required.
The NRST Manager shapes the NRST assertion during a programmable time, thus controlling external device resets.
The Reset Controller Mode Register (RSTC_MR), allowing the configuration of the Reset Controller, is powered with
VDDIO, so that its configuration is saved as long as VDDIO is on.
VDDIO, so that its configuration is saved as long as VDDIO is on.
14.4.2 NRST Manager
After power-up, NRST is an output during the ERSTL time period defined in the RSTC_MR. When ERSTL has elapsed,
the pin behaves as an input and all the system is held in reset if NRST is tied to GND by an external signal.
the pin behaves as an input and all the system is held in reset if NRST is tied to GND by an external signal.
The NRST Manager samples the NRST input pin and drives this pin low when required by the Reset State Manager.
Figure 14-2. NRST Manager
14.4.2.1 NRST Signal or Interrupt
The NRST Manager samples the NRST pin at Slow Clock speed. When the line is detected low, a User Reset is reported
to the Reset State Manager.
to the Reset State Manager.
However, the NRST Manager can be programmed to not trigger a reset when an assertion of NRST occurs. Writing the
bit URSTEN at 0 in RSTC_MR disables the User Reset trigger.
bit URSTEN at 0 in RSTC_MR disables the User Reset trigger.
The level of the pin NRST can be read at any time in the bit NRSTL (NRST level) in RSTC_SR. As soon as the pin NRST
is asserted, the bit URSTS in RSTC_SR is set. This bit clears only when RSTC_SR is read.
is asserted, the bit URSTS in RSTC_SR is set. This bit clears only when RSTC_SR is read.
The Reset Controller can also be programmed to generate an interrupt instead of generating a reset. To do so, the bit
URSTIEN in RSTC_MR must be written at 1.
URSTIEN in RSTC_MR must be written at 1.
External Reset Timer
URSTS
URSTEN
ERSTL
exter_nreset
URSTIEN
RSTC_MR
RSTC_MR
RSTC_MR
RSTC_SR
NRSTL
nrst_out
NRST
rstc_irq
Other
interrupt
sources
user_reset