Rainbow-electronics ATtiny43U Manual do Utilizador descarregar pdf (Página 49)

8048B–AVR–03/09

9.2 Reset Sources

The ATtiny43U has four sources of reset:

• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset

threshold (V

POT

• External Reset. The MCU is reset when a low level is present on the RESET

pin for longer

than the minimum pulse length when RESET

function is enabled.

• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the

Watchdog is enabled.

• Brown-out Reset. The MCU is reset when the supply voltage V

is below the Brown-out

Reset threshold (V

BOT

) and the Brown-out Detector is enabled.

9.3 Power-on Reset

A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level

is defined in Table 20-4 on page 158. The POR is activated whenever V

is below the detection

level. The POR circuit can be used to trigger the Start-up Reset, as well as to detect a failure in

supply voltage.

A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the

Power-on Reset threshold voltage invokes the delay counter, which determines how long the

device is kept in RESET after V

rise. The RESET signal is activated again, without any delay,

when V

decreases below the detection level.

Figure 9-2. MCU Start-up, RESET

Tied to V

Figure 9-3. MCU Start-up, RESET Extended Externally

RESET

TIME-OUT

INTERNAL

RESET

TOUT

POT

RST

RESET

TIME-OUT

INTERNAL

RESET

TOUT

POT

RST

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