ATtiny261A datasheet(41/292 Pages) ATMEL

41 / 292 page

8197A–AVR–10/09

ATtiny261A/461A/861A

8.2.2

External Reset

An External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer

than the minimum pulse width (see “System and Reset Characteristics” on page 187) will gener-

ate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a

reset. When the applied signal reaches the Reset Threshold Voltage – VRST – on its positive

edge, the delay counter starts the MCU after the Time-out period – tTOUT – has expired.

Figure 8-4.

External Reset During Operation

8.2.3

Brown-out Detection

A Brown-out Detection (BOD) circuit monitors the VCC level during operation by comparing it to a

fixed trigger level. The trigger level for the BOD can be selected by the BODLEVEL Fuses. The

trigger level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis on the

detection level should be interpreted as VBOT+ = VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.

When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure

8-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level

(VBOT+ in Figure 8-5), the delay counter starts the MCU after the Time-out period tTOUT has

expired.

The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-

ger than tBOD given in “System and Reset Characteristics” on page 187.

Figure 8-5.

Brown-out Reset During Operation

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

ATtiny261A Scheda tecnica(PDF) 41 Page - ATMEL Corporation