SAM4CP [DATASHEET]
43051E–ATPL–08/14
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6.7
Shutdown (SHDN) Pin
The SHDN pin reflects the MCU backup mode of operation: when the MCU is in backup mode, SHDN = 0, otherwise
SHDN = 1 (VDDBU). This pin is designed to control the enable pin of the main external voltage regulator. When the MCU
enters backup mode, the SHDN pin disables the external voltage regulator and, upon wake-up event, it re-enables the
voltage regulator. The SHDN pin is used to control an external main voltage regulator and/or power switch when entering
backup mode.
The SHDN pin is asserted low when the VROFF bit in the Supply Controller Control Register (SUPC_CR) is set to 1.
6.8
Force Wake-up (FWUP) Pin
The FWUP pin can be used as a wake-up source in all low-power modes as it is supplied by VDDBU.
6.9
ERASE Pin
The ERASE pin is used to reinitialize the Flash content (and some of its NVM bits) to an erased state (all bits read as
logic level 1). The ERASE pin integrates a pull-down resistor of about 100 k
into GND, so that it can be left
unconnected for normal operations.
This pin is debounced by SLCK to improve the glitch tolerance. When the ERASE pin is tied high during less than
100 ms, it is not taken into account. The pin must be tied high during more than 220 ms to perform a Flash erase
operation.
The ERASE pin is a system I/O pin and can be used as a standard I/O. At start-up, the ERASE pin is not configured as
a PIO pin. If the ERASE pin is used as a standard I/O, the start-up level of this pin must be low to prevent unwanted
erasing. Refer to
Section 11.3 “APB/AHB Bridge” on page 44
. If the ERASE pin is used as a standard I/O output,
asserting the pin to low does not erase the Flash.
To avoid unexpected erase at power-up, a minimum ERASE pin assertion time is required. This time is defined in the AC
Flash Characteristics in the Electrical Characteristics.
The erase operation is not performed when the system is in Wait mode with the Flash in Deep-power-down mode.
To make sure that the erase operation is performed after power-up, the system must not reconfigure the ERASE pin as
GPIO or enter Wait mode with Flash in Deep-power-down mode before the ERASE pin assertion time has elapsed.
With the following sequence, in any case, the erase operation is performed:
1.
Assert the ERASE pin (High).
2.
Assert the NRST pin (Low).
3.
Power cycle the device.
4.
Maintain the ERASE pin high for at least the minimum assertion time.