at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 54

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

8.2.2
8.3
8.3.1
54
Internal Voltage Reference
AT90PWM81
MCU Control Register – MCUCR
Bandgap and Internal Voltage Reference Enable Signals and Start-up Time
• 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.
• Bit 3– RSTDIS: Reset Pin Disable
Thanks to RSTDIS in MCUCR Sfr, the reset function can be disabled, leaving this pin for functional
purpose.
AT90PWM81 features an internal bandgap reference. This bandgap reference is used for Brown-out
Detection and can be used as analog input for the analog comparators or the ADC.
The internal voltage reference for the DAC and/or the ADC and the comparators is derived from this
bandgap voltage. see
The Vref voltage is configured thanks to the REFS1 and REFS0 bits in the ADMUX register; see
Multiplexer Register – ADMUX” on page 216
The bandgap and the internal voltage reference characteristics is given on
reference is not always turned on. The bandgap and the internal reference is on during the following
situations:
Bit
Read/Write
Initial Value
1.
2.
3.
4.
– When the RSTDIS bit is written to zero, the reset signal is active.
– When the RSTDIS bit is written to one, the reset signal is inactive.
When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
When the internal reference is selected (REFS1 = 1)
When the bandgap reference is connected to the Analog Comparator.
When the ADC is enabled.
7
–
R
0
“On Chip voltage Reference and Temperature sensor overview” on page 189
6
–
R
0
5
–
R
0
4
PUD
R/W
0
3
RSTDIS
R/W
0
2
CKRC81
R/W
0
Table
1
IVSEL
R/W
0
8-4. To save power, the
0
IVCE
R/W
0
7734M–AVR–03/10
MCUCR
“ADC