Rainbow-electronics ATmega8HVD Manuel d'utilisateur télécharger pdf (Page 41)

8052B–AVR–09/08

ATmega4HVD/8HVD

guaranteed and the chip should be forced into Power-off mode. The algorithm used for switch-

ing between the two V

BLOT

levels is illustrated Figure 10-4 on page 41. As long as BLOD is set,

the V

BLOT, START-UP

level will always be selected.

Figure 10-4. BLOD levels switching

Notice that during the Power-On Reset start-up sequence, a Black-out detection will only gen-

erate a normal reset. The chip will not enter Power-off in this case. This is illustrated in Figure

10-5 on page 41. See TBD for details on Power-on Reset and start-up sequence.

Figure 10-5. BLOD detection with POR

In normal operation, when V

REG

decreases to a value below the trigger level, the Black-out

Reset is immediately activated. After a fixed delay of T

BLODTOUT

the chip will enter Power-off

mode, see Figure 10-6 on page 41 and ”System and Reset Characteristics” on page 144. Any

ongoing operations, including EEPROM write sequences that were started while V

REG

was

above V

BLOD

, will be aborted. The result of an ongoing EEPROM write operation will be invalid.

A charger must be connected to start up the chip from Power-off.

The BLOD circuit will only detect a drop in V

REG

if the voltage stays below the trigger level for

longer than t

BLOD

given in ”System and Reset Characteristics” on page 144.

Figure 10-6. Black-out Reset During Operation

BLOD

VBLOT, NORMAL

VBLOT,STARTUP

BLOD

DETECTION

BLOD LEVEL

VREG

BLOD_PWROFF

BLOD

POR

reset

Power-on

Internal Reset

BLOT

BLODTOUT

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 167 168

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Rainbow-electronics ATmega8HVD Manuel d'utilisateur Page 41

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