ATmega8U2/16U2/32U2
Table 25-2. Lock Bit Protection Modes(1)(2) (Continued)
Memory Lock Bits
Protection Type
BLB1 Mode
BLB12
BLB11
No restrictions for SPM or (E)LPM accessing the Boot Loader
section.
1
2
1
1
1
0
SPM is not allowed to write to the Boot Loader section.
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.
3
0
0
(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.
4
0
1
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.
Table 25-3. Extended Fuse Byte
Fuse Low Byte
Bit No
Description
Default Value : 0xF4
–
–
–
–
7
6
5
4
3
2
1
0
–
1
–
1
–
1
–
1
HWBE
Hardware Boot Enable
Brown-out Detector trigger level
Brown-out Detector trigger level
Brown-out Detector trigger level
0 (programmed)
1 (unprogrammed)
0 (programmed)
0 (programmed)
BODLEVEL2(1)
BODLEVEL1(1)
BODLEVEL0(1)
Note:
1. See “System and Reset Characteristics” on page 267 for BODLEVEL Fuse decoding.
247
7799D–AVR–11/10
ATMEL [ ATMEL ]
