ATMEGA8U2_14 Datasheet, PDF (231/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

ATmega8U2/16U2/32U2
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.
Table 23-4. Boot Reset Fuse⁽¹⁾
BOOTRST Reset Address
1
Reset Vector = Application Reset (address 0x0000)
0
Reset Vector = Boot Loader Reset (see Table 23-8 on page 239)
23.6.3
Note: 1. “1” means unprogrammed, “0” means programmed
External Hardware conditions
The Hardware Boot Enable Fuse (HWBE) can be programmed (See Table 23-5) so that upon
special hardware conditions under reset, the bootloader execution is forced after reset.
Table 23-5.
HWBE
1
0
Hardware Boot Enable Fuse⁽¹⁾
Reset Address
PD7/HWB pin can not be used to force Boot Loader execution after reset
PD7/HWB pin is used during reset to force bootloader execution after reset
Note: 1. “1” means unprogrammed, “0” means programmed
When the HWBE fuse is enable the PD7/HWB pin is configured as input during reset and sam-
pled during reset rising edge. When PD7/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
23-3).
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