Internal voltage reference, Voltage reference enable signals and start-up time, Atmega169v/l – Rainbow Electronics Atmega169L User Manual

Page 41

ATmega169V/L

2514A–AVR–08/02

• 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.

Internal Voltage
Reference

ATmega169 features an internal bandgap reference. This reference is used for Brown-
out Detection, and it can be used as an input to the Analog Comparator or the ADC.

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 19. 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.

Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the
user must always allow the reference to start up before the output from the Analog Com-
parator or ADC 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.

Note:

1. Values are guidelines only. Actual values are TBD.

Table 19. Internal Voltage Reference Characteristics

(1)

Symbol

Parameter

Condition

Min

Typ

Max

Units

Bandgap reference voltage

TBD

1.1

TBD

Bandgap reference start-up time

TBD

µs

Bandgap reference current
consumption

TBD

µA