AT91SAM7S256-AU-001 Atmel, AT91SAM7S256-AU-001 Datasheet - Page 29

• Manufacturer Part Number: AT91SAM7S256-AU-001
• Description: IC ARM7 MCU 32BIT 256K 64LQFP
• Manufacturer: Atmel
• Series: AT91SAMr

Specifications of AT91SAM7S256-AU-001

• Package / Case: 64-LQFP
• Voltage - Supply (vcc/vdd): 1.65 V ~ 1.95 V
• Operating Temperature: -40°C ~ 85°C
• Speed: 55MHz
• Number Of I /o: 32
• Core Processor: ARM7
• Program Memory Type: FLASH
• Ram Size: 64K x 8
• Program Memory Size: 256KB (256K x 8)
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Peripherals: Brown-out Detect/Reset, DMA, POR, PWM, WDT
• Connectivity: I²C, SPI, SSC, UART/USART, USB
• Core Size: 16/32-Bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Other names: AT91SAM7S256AU001

9.1
9.1.1
6175FS–ATARM–03-Dec-07
Reset Controller
Brownout Detector and Power-on Reset
The Reset Controller is based on a power-on reset cell and one brownout detector. It gives the
status of the last reset, indicating whether it is a power-up reset, a software reset, a user reset, a
watchdog reset or a brownout reset. In addition, it controls the internal resets and the NRST pin
open-drain output. It allows to shape a signal on the NRST line, guaranteeing that the length of
the pulse meets any requirement.
Note that if NRST is used as a reset output signal for external devices during power-off, the
brownout detector must be activated.
The AT91SAM7S Series embeds a brownout detection circuit and a power-on reset cell. Both
are supplied with and monitor 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
VDDCORE power supply.
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 level during operation by comparing it 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.
Only VDDCORE is monitored, as a voltage drop on VDDFLASH or any other power supply of
the device cannot affect the Flash.
When the brownout detector is enabled and VDDCORE decreases to a value below the trigger
level (Vbot-, defined as Vbot - hyst/2), the brownout output is immediately activated.
When VDDCORE increases above the trigger level (Vbot+, defined as Vbot + 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 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.
The brownout detector is low-power, as it consumes less than 20 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.
AT91SAM7S Series Summary
29