
44
AT90PWM216/316 [DATASHEET]
7710H–AVR–07/2013
8.7
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.
8.8
Internal Voltage Reference
AT90PWM216/316 features an internal bandgap reference. This reference is used for Brown-out Detection. The
VREF 2.56V reference to the ADC, DAC or Analog Comparators is generated from the internal bandgap reference.
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.
8.8.1
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 8-4. To save power, the reference is not always turned on. The reference is on during the following
situations:
1.
When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2.
When the ADC is enabled.
3.
When the DAC is enabled.
Thus, when the BOD is not enabled, after 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.
Bit
7
65
43
21
0
–
WDRF
BORF
EXTRF
PORF
MCUSR
Read/Write
R
R/W
Initial Value
0
See Bit Description