SAM7X128_14 Datasheet, PDF (25/662 Pages) ATMEL Corporation – ARM-based Flash MCU

9.1 Reset Controller
 Based on one power-on reset cell and one brownout detector
 Status of the last reset, either Power-up Reset, Software Reset, User Reset, Watchdog Reset, Brownout Reset
 Controls the internal resets and the NRST pin output
 Allows to shape a signal on the NRST line, guaranteeing that the length of the pulse meets any requirement.
9.1.1
Brownout Detector and Power-on Reset
The SAM7X512/256/128 embeds one brownout detection circuit and a power-on reset cell. The power-on reset is
supplied with and monitors VDDCORE.
Both signals are provided to the Flash to prevent any code corruption during power-up or power-down sequences or if
brownouts occur on the power supplies.
The power-on reset cell has a limited-accuracy threshold at around 1.5V. Its output remains low during power-up until
VDDCORE goes over this voltage level. This signal goes to the reset controller and allows a full re-initialization of the
device.
The brownout detector monitors the VDDCORE and VDDFLASH levels during operation by comparing them to a fixed
trigger level. It secures system operations in the most difficult environments and prevents code corruption in case of
brownout on the VDDCORE or VDDFLASH.
When the brownout detector is enabled and VDDCORE decreases to a value below the trigger level (Vbot18-, defined as
Vbot18 - hyst/2), the brownout output is immediately activated.
When VDDCORE increases above the trigger level (Vbot18+, defined as Vbot18 + hyst/2), the reset is released. The
brownout detector only detects a drop if the voltage on VDDCORE stays below the threshold voltage for longer than
about 1µs.
The VDDCORE threshold voltage has a hysteresis of about 50 mV, to ensure spike free brownout detection. The typical
value of the brownout detector threshold is 1.68V with an accuracy of ± 2% and is factory calibrated.
When the brownout detector is enabled and VDDFLASH decreases to a value below the trigger level (Vbot33-, defined
as Vbot33 - hyst/2), the brownout output is immediately activated.
When VDDFLASH increases above the trigger level (Vbot33+, defined as Vbot33 + hyst/2), the reset is released. The
brownout detector only detects a drop if the voltage on VDDCORE stays below the threshold voltage for longer than
about 1µs.
The VDDFLASH threshold voltage has a hysteresis of about 50 mV, to ensure spike free brownout detection. The typical
value of the brownout detector threshold is 2.80V with an accuracy of ± 3.5% and is factory calibrated.
The brownout detector is low-power, as it consumes less than 28 µA static current. However, it can be deactivated to
save its static current. In this case, it consumes less than 1µA. The deactivation is configured through the GPNVM bit 0 of
the Flash.
SAM7X Series [DATASHEET] 25
6120K–ATARM–11-Feb-14