AT90PWM2 datasheet(50/365 Pages) ATMEL

50 / 365 page

4317K–AVR–03/2013

AT90PWM2/3/2B/3B

Figure 9-6.

Watchdog Reset During Operation

9.0.7

MCU Status Register – MCUSR

The MCU Status Register provides information on which reset source caused an MCU reset.

• Bit 3 – WDRF: Watchdog Reset Flag

This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a

logic zero to the flag.

• Bit 2 – BORF: Brown-out Reset Flag

This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a

logic zero to the flag.

• Bit 1 – EXTRF: External Reset Flag

This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a

logic zero to the flag.

• Bit 0 – PORF: Power-on Reset Flag

This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.

To make use of the Reset flags to identify a reset condition, the user should read and then reset

the MCUSR as early as possible in the program. If the register is cleared before another reset

occurs, the source of the reset can be found by examining the reset flags.

9.1

Internal Voltage Reference

AT90PWM2/2B/3/3B features an internal bandgap reference (1.1V). This reference is used for

Brown-out Detection. A 2.56V voltage reference is generated thanks to the bandgap

, it can be used as

a voltage reference for the DAC and/or the ADC, and can also be used as analog input for the

analog comparators. In order to use the internal Vref, it is necessary to configure it thanks to the

REFS1 and REFS0 bits in the ADMUX register and to set an analog feature which requires it.

9.1.1

Voltage Reference Enable Signals and Start-up Time

The voltage reference has a start-up time that may influence the way it should be used. The

start-up time is given in Table 9-4. To save power, the reference is not always turned on. The

reference is on during the following situations:

Bit

–

WDRF

BORF

EXTRF

PORF

MCUSR

Read/Write

R/W

Initial Value

See Bit Description

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