atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 49

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

7.3
7.3.1
7.3.2
7647A–AVR–02/08
Internal Voltage Reference
Voltage Reference Enable Signals and Start-up Time
Voltage Reference Characteristics
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.
ATmega32/64/M1/C1 features an internal bandgap reference. This reference is used for Brown-
out DetectionDetection, and it can be used as an input to the Analog Comparators or the ADC.
The V
nal bandgap reference.
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in
reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
3. When the ADC is enabled.
4. 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 Compar-
ator 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.
Table 7-4.
Note:
Symbol
V
ACBG bit in ACSR).
t
I
BG
BG
BG
REF
1. Values are guidelines only.
2.56V reference to the ADC, DAC or Analog Comparators is generated from the inter-
Parameter
Bandgap reference voltage
Bandgap reference start-up time
Bandgap reference current
consumption
Internal Voltage Reference Characteristics
Table
7-4. To save power, the reference is not always turned on. The
Condition
ATmega32/64/M1/C1
(1)
Min.
Typ.
1.1
40
15
Max.
Units
µA
µs
V
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