AT90PWM2 datasheet(49/365 Pages) ATMEL

49 / 365 page

AT90PWM2/3

4317B–AVR–02/05

• 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.

Internal Voltage

Reference

AT90PWM2/3 features an internal bandgap reference. This reference is used for Brown-

out Detection. It can also be used as a voltage reference for the DAC and/or the ADC,

and can 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

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 17. To save power, the reference is not always turned

on. The reference is on during the following situations:

When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).

When the bandgap reference is connected to the Analog Comparator (by setting

the ACBG bit in ACSR).

When the ADC is enabled.

When the DAC is enabled.

Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC or

the DAC, the user must always allow the reference to start up before the output from the

Analog Comparator or ADC or DAC is used. To reduce power consumption in Power-

down mode, the user can avoid the three conditions above to ensure that the reference

is turned off before entering Power-down mode.

Voltage Reference

Characteristics

Note:

1. Values are guidelines only.

Table 17. Internal Voltage Reference Characteristics(1)

Symbol

Parameter

Condition

Min.

(TBD)

Typ.

(TBD)

Max.

(TBD)Units

VBG

Bandgap reference voltage

TBD

tBG

Bandgap reference start-up time

TBD

µs

IBG

Bandgap reference current

consumption

TBD

µA

AT90PWM2 Datasheet(PDF) 49 Page - ATMEL Corporation

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