Rainbow-electronics ATmega8515L Instrukcja Użytkownika Pobierz pdf (Strona 42)

ATmega8515(L)

2512A–AVR–04/02

System Control and

Reset

Resetting the AVR During Reset, all I/O Registers are set to their initial values, and the program starts exe-

cution from theReset Vector.Theinstruction placed at theReset Vector must bea

RJMPinstruction to the reset handling routine. If the program never enables an interrupt

source, the InterruptVectors arenotused, andregularprogram code can be placed at

these locations.This is alsothe caseif theReset Vector is in theApplication section

whilethe InterruptVectors areinthe Boot section or viceversa. The circuit diagram in

Figure21shows the reset logic.Table18defines theelectricalparameters of the reset

circuitry.

The I/Oports of theAVRareimmediately reset to their initialstate when a reset source

goes active. Thisdoes not requireanyclock sourcetobe running.

After all reset sourceshave gone inactive, a delaycounter is invoked, stretching the

internalreset. This allows the power to reach a stable levelbeforenormal operation

starts.Thetime-out period of the delaycounter isdefinedbytheuser through the

CKSEL Fuses.The different selectionsfor the delayperiod are presented in “Clock

Sources”onpage 32.

Reset Sources The ATmega8515 hasfoursources ofreset:

•Power-on Reset. The MCU isreset when the supply voltage isbelow thePower-on

Reset threshold (V

POT

• External Reset. The MCU isreset when a lowlevel ispresent on theRESET

pin for

longer than the minimum pulse length.

• Watchdog Reset. The MCU isreset when the Watchdog Timerperiod expires and

the Watchdog is enabled.

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

isbelow the

Brown-out Reset threshold (V

BOT

) and the Brown-out Detector is enabled.

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 222 223

Brak uwag

Rainbow-electronics ATmega8515L Instrukcja Użytkownika Strona 42