AT90USB646 datasheet(357/434 Pages) ATMEL

357 / 434 page

357

7593A–AVR–02/06

AT90USB64/128

is programmed, the Reset Vector will always point to the Boot Loader Reset and the fuse can

only be changed through the serial or parallel programming interface.

Note:

1. “1” means unprogrammed, “0” means programmed

28.5.3

External Hardware conditions

The Hardware Boot Enable Fuse (HWBE) can be programmed (See Table 28-5) so that upon

special hardware conditions under reset, the bootloader execution is forced after reset.

Note:

1. “1” means unprogrammed, “0” means programmed

When the HWBE fuse is enable the ALE/HWB pin is configured as input during reset and sam-

pled during reset rising edge. When ALE/HWB pin is ‘0’ during reset rising edge, the reset vector

will be set as the Boot Loader Reset address and the Boot Loader will be executed (See Figures

28-3).

Table 28-4.

Boot Reset Fuse

(1)

BOOTRST

Reset Address

Reset Vector = Application Reset (address 0x0000)

Reset Vector = Boot Loader Reset (see Table 28-8 on page 366)

Table 28-5.

Hardware Boot Enable Fuse

(1)

HWBE

Reset Address

1ALE/HWB pin can not be used to force Boot Loader execution after reset

0ALE/HWB pin is used during reset to force bootloader execution after reset

AT90USB646 Datasheet(PDF) 357 Page - ATMEL Corporation