Datasheet

347
7766E–AVR–04/10
ATmega16U4/ATmega32U4
Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
28.2 Fuse Bits
The ATmega16U4/ATmega32U4 has three bytes. Table 28-3 - Table 28-5 describe briefly the
functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses
are read as logical zero, “0”, if they are programmed.
Note: 1. See Table 8-2 on page 52 for BODLEVEL Fuse decoding.
BLB1 Mode BLB12 BLB11
111
No restrictions for SPM or (E)LPM accessing the Boot
Loader section.
2 1 0 SPM is not allowed to write to the Boot Loader section.
300
SPM is not allowed to write to the Boot Loader section,
and (E)LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
401
(E)LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
Table 28-2. Lock Bit Protection Modes
(1)(2)
(Continued)
Memory Lock Bits Protection Type
Table 28-3. Extended Fuse Byte
Fuse Low Byte Bit No Description Default Value
–7– 1
–6– 1
–5– 1
–4– 1
HWBE 3 Hardware Boot Enable 0 (programmed)
BODLEVEL2
(1)
2 Brown-out Detector trigger level 0 (programmed)
BODLEVEL1
(1)
1 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL0
(1)
0 Brown-out Detector trigger level 1 (unprogrammed)