Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
116
16.6 Functional Description
The Shutdown Controller manages the main power supply. To do so, it is supplied with VDDBU and manages
wakeup input pins and one output pin, SHDN.
A typical application connects the pin SHDN to the shutdown input of the DC/DC Converter providing the main
power supplies of the system, and especially VDDCORE and/or VDDIO. The wakeup inputs (WKUP0) connect to
any push-buttons or signal that wake up the system.
The software is able to control the pin SHDN by writing the Shutdown Control Register (SHDW_CR) with the bit
SHDW at 1. The shutdown is taken into account only 2 slow clock cycles after the write of SHDW_CR. This
register is password-protected and so the value written should contain the correct key for the command to be
taken into account. As a result, the system should be powered down.
A level change on WKUP0 is used as wakeup. Wakeup is configured in the Shutdown Mode Register
(SHDW_MR). The transition detector can be programmed to detect either a positive or negative transition or any
level change on WKUP0. The detection can also be disabled. Programming is performed by defining WKMODE0.
Moreover, a debouncing circuit can be programmed for WKUP0. The debouncing circuit filters pulses on WKUP0
shorter than the programmed number of 16 SLCK cycles in CPTWK0 of the SHDW_MR. If the programmed level
change is detected on a pin, a counter starts. When the counter reaches the value programmed in the
corresponding field, CPTWK0, the SHDN pin is released. If a new input change is detected before the counter
reaches the corresponding value, the counter is stopped and cleared. WAKEUP0 of the Status Register
(SHDW_SR) reports the detection of the programmed events on WKUP0 with a reset after the read of SHDW_SR.
The Shutdown Controller can be programmed so as to activate the wakeup using the RTT alarm (the detection of
the rising edge of the RTT alarm is synchronized with SLCK). This is done by writing the SHDW_MR using the
RTTWKEN fields. When enabled, the detection of the RTT alarm is reported in the RTTWK bit of the SHDW_SR
Status register. It is reset after the read of SHDW_SR. When using the RTT alarm to wake up the system, the user
must ensure that the RTT alarm status flag is cleared before shutting down the system. Otherwise, no rising edge
of the status flag may be detected and the wakeup fails.