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AT91SAM7X256 Datasheet(PDF) 22 Page - ATMEL Corporation

No. de Pieza. AT91SAM7X256
Descripción  AT91 ARM Thumb-based Microcontrollers
Descarga  664 Pages
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Fabricante  ATMEL [ATMEL Corporation]
Página de inicio  http://www.atmel.com
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AT91SAM7X256 Datasheet(HTML) 22 Page - ATMEL Corporation

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6120D–ATARM–02-Feb-06
AT91SAM7X256/128 Preliminary
10.2
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.
10.2.1
Brownout Detector and Power-on Reset
The AT91SAM7X256/X128 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 con-
troller 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 environ-
ments 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 brown-
out 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 brown-
out 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 deac-
tivation is configured through the GPNVM bit 0 of the Flash.


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