Rainbow Electronics AT91CAP9S250A - Manual (Page 122)

122
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
A typical application connects the pin SHDN to the shutdown input of the DC/DC Converter pro-
viding the main power supplies of the system, and especially VDDCORE and/or VDDIO. The
wake-up 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 wake-up. Wake-up 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. Pro-
gramming 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 register. 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 corre-
sponding 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 register using the RTTWKEN fields. When enabled, the detec-
tion 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 wake-up fails.