Rainbow-electronics ATmega8515L Uživatelský manuál stáhnout pdf (Strana 47)

ATmega8515(L)

2512A–AVR–04/02

Internal Voltage

Reference

ATmega8515 features an internalbandgapreference. Thisreferenceis usedforBrown-

out Detection, and it can beused as an input to theAnalog Comparator.

Voltage Reference Enable

Signals and Start-up Time

Thevoltage reference has a start-up time that may influencethe way it should beused.

The start-up time is given in Table19.Tosave power, the referenceis not always turned

on. The referenceis on during the following situations:

1. When the BOD is enabled(byprogramming the BODEN Fuse).

2. When the bandgapreferenceisconnected to theAnalog Comparator(bysetting

theACBG bit in ACSR).

Thus, when the BOD is not enabled, aftersetting theACBG bit, theuser mustalways

allow the referencetostartupbeforethe output from theAnalog Comparator is used.To

reduce powerconsumption in Power-downmode, theusercan avoid thetwo conditions

above to ensurethat the referenceis turned off beforeentering Power-downmode.

Watchdog Timer The Watchdog Timer isclockedfrom a separate On-chipOscillatorwhich runs at

1 MHz.This is thetypicalfrequency at V

= 5V. See characterization data for typical

values at other V

levels. By controlling the Watchdog Timerprescaler, the Watchdog

Reset intervalcan beadjusted asshowninTable21onpage 49.The WDR–Watchdog

Reset – instruction resets the Watchdog Timer.The Watchdog Timer is also reset when

it isdisabled andwhen a Chip Reset occurs. Eight different clock cycle periods can be

selected to determine the reset period. If the reset period expireswithout another

Watchdog Reset, the ATmega8515 resets and executesfrom theReset Vector. For tim-

ing details on the Watchdog Reset,refer to page 46.

To prevent unintentionaldisabling of the Watchdog or unintentionalchange of time-out

period, three different safetylevels are selectedbythe FusesS8515C andWDTON as

showninTable 20. Safetylevel 0 corresponds to the setting in AT90S4414/8515. There

is no restriction on enabling the WDTinany of the safetylevels.Refer to “Timed

SequencesforChanging the Configuration of the Watchdog Timer”onpage 50 for

details.

Table 19. Internal Voltage Reference Characteristics

Symbol Parameter Min Typ Max Units

Bandgapreferencevoltage 1.15 1.23 1.35V

Bandgapreference start-up time 40 70 µs

Bandgapreference current consumption 10 µA

1 2 ... 42 43 44 45 46 47 48 49 50 51 52 ... 222 223

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Rainbow-electronics ATmega8515L Uživatelský manuál Strana 47