ATTINY15L View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

ATTINY15L

8-bit Microcontroller with 1K Byte Flash

Atmel Corporation 

MCU Status Register –

MCUSR

Internal Voltage

Reference

Voltage Reference Enable

Signals and Start-up Time

The MCU Status Register provides information on which reset source caused an MCU

Reset.

Bit

7

6

5

4

3

2

1

0

$34

–

–

–

–

WDRF BORF EXTRF PORF MCUSR

Read/Write

R

R

R

R

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

See Bit Description

• Bit 7..4 – Res: Reserved Bits

These bits are reserved bits in the ATtiny15L and always read as zero.

• Bit 3 – WDRF: Watchdog Reset Flag

This bit is set (one) if a Watchdog Reset occurs. The bit is reset (zero) by a Power-on

Reset, or by writing a logical “0” to the flag.

• Bit 2 – BORF: Brown-out Reset Flag

This bit is set (one) if a Brown-out Reset occurs. The bit is reset (zero) by a Power-on

Reset, or by writing a logical “0” to the flag.

• Bit 1 – EXTRF: External Reset Flag

This bit is set (one) if a External Reset occurs. The bit is reset (zero) by a Power-on

Reset, or by writing a logical “0” to the flag.

• Bit 0 – PORF: Power-on Reset Flag

This bit is set (one) if a Power-on Reset occurs. The bit is reset (zero) by writing a logical

“0” 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.

ATtiny15L features an internal bandgap reference with a nominal voltage of 1.22V. This

reference is used for Brown-out Detection, and it can be used as an input to the Analog

Comparator. The 2.56V reference to the ADC is generated from the internal bandgap

reference.

The voltage reference has a start-up time that may influence the way it should be used.

The maximum start-up time is 10 µs. 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 BODEN Fuse).

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

the AINBG bit in ACSR).

3. When the ADC is enabled.

Thus, when the BOD is not enabled, after setting the AINBG bit, the user must always

allow the reference to start-up before the output from the Analog Comparator is used.

The bandgap reference uses typically 10 µA, and to reduce power consumption in

Power-down mode, the user can avoid the three conditions above to ensure that the ref-

erence is turned off before entering Power-down mode.

18 ATtiny15L

1187H–AVR–09/07

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