Datasheet
2017 Microchip Technology Inc. DS60001516A-page 113
SAM9G20
17.5 Functional Description
The Shutdown Controller manages the main power supply. To do so, it is supplied with VDDBU and manages wake-up 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 sys-
tem, and especially VDDCORE and/or VDDIO. The wake-up inputs (WKUP0) connect to any push-buttons or signal that wake up the sys-
tem.
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 wake-up. Wake-up is configured in the Shutdown Mode Register (SHDW_MR). The transition detec-
tor can be programmed to detect either a positive or negative transition or any level change on WKUP0. The detection can also be dis-
abled. 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 pro-
grammed 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 wake-up 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. Oth-
erwise, no rising edge of the status flag may be detected and the wake-up fails.