atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 355

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

28.5.3
7766A–AVR–03/08
External Hardware conditions
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 28-4.
Note:
The Hardware Boot Enable Fuse (HWBE) can be programmed (See
special hardware conditions under reset, the bootloader execution is forced after reset.
Table 28-5.
Note:
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).
Figure 28-3. Boot Process Description
BOOTRST
HWBE
1
0
1
0
1. “1” means unprogrammed, “0” means programmed
1. “1” means unprogrammed, “0” means programmed
Boot Reset Fuse
Hardware Boot Enable Fuse
Reset Address
Reset Vector = Application Reset (address 0x0000)
Reset Vector = Boot Loader Reset (see
Reset Address
ALE/HWB pin can not be used to force Boot Loader execution after reset
ALE/HWB pin is used during reset to force bootloader execution after reset
Reset Vector = Application Reset
BOOTRST ?
HWBE
?
(1)
(1)
ALE/HWB
RESET
Table 28-8 on page
Ext. Hardware
Conditions ?
Reset Vector =Boot Lhoader Reset
t
SHRH
ATmega32U4
Table
364)
28-5) so that upon
t
HHRH
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