Rainbow-electronics Atmega169L Manuel d'utilisateur télécharger pdf (Page 39)

ATmega169V/L

2514A–AVR–08/02

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

than the minimum pulse width (see Table 16) will generate 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 – V

RST

– on its positive edge, the delay

counter starts the MCU after the Time-out period – t

TOUT

– has expired.

Figure 17. External Reset During Operation

Brown-out Detection ATmega169 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

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 V

BOT+

BOT

HYST

/2 and V

BOT-

BOT

-V

HYST

/2.

Note: 1. V

BOT

may be below nominal minimum operating voltage for some devices. For

devices where this is the case, the device is tested down to V

BOT

during the

production test. This guarantees that a Brown-Out Reset will occur before V

drops

to a voltage where correct operation of the microcontroller is no longer guaranteed.

The test is performed using BODLEVEL = 110 for ATmega169V and

BODLEVEL = 101 for ATmega169L.

Table 17. BODLEVEL Fuse Coding

(1)

BODLEVEL 2..0 Fuses Min V

BOT

Typ V

BOT

Max V

BOT

Units

111 BOD Disabled

110 1.8

V101 2.7

100 4.3

011

Reserved

010

001

000

Table 18. Brown-out Characteristics

Symbol Parameter Min Typ Max Units

HYST

Brown-out Detector Hysteresis 50 mV

BOD

Min Pulse Width on Brown-out Reset ns

1 2 ... 34 35 36 37 38 39 40 41 42 43 44 ... 316 317

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Rainbow-electronics Atmega169L Manuel d'utilisateur Page 39

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