Datasheet

247
7799D–AVR–11/10
ATmega8U2/16U2/32U2
Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
25.2 Fuse Bits
The ATmega8U2/16U2/32U2 has three Fuse bytes. Table 25-3 - Table 25-5 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 “System and Reset Characteristics” on page 267 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 25-2. Lock Bit Protection Modes
(1)(2)
(Continued)
Memory Lock Bits Protection Type
Table 25-3. Extended Fuse Byte
Fuse Low Byte Bit No Description Default Value : 0xF4
–7– 1
–6– 1
–5– 1
–4– 1
HWBE 3 Hardware Boot Enable 0 (programmed)
BODLEVEL2
(1)
2 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL1
(1)
1 Brown-out Detector trigger level 0 (programmed)
BODLEVEL0
(1)
0 Brown-out Detector trigger level 0 (programmed)