Datasheet

354
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
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 device has three bytes. Table 28-3 to Table 28-5 on page 355 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.
Notes: 1. See Table 8-1 on page 53 for BODLEVEL Fuse decoding.
2. “1” means unprogrammed, “0” means programmed.
4 0 1
(E)LPM executing from the Boot Loader section is not allowed to
read from the Application section. If Interrupt Vectors are placed in
the Boot Loader section, interrupts are disabled while executing
from the Application section.
BLB1 Mode BLB12 BLB11
1 1 1
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.
3 0 0
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.
4 0 1
(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)
Memory Lock Bits Protection Type
Table 28-3. Extended Fuse Byte
(1)(2)
Fuse Low Byte Bit No Description Default Value
ATmega16/32U4 ATmega16/32U4RC
– 7 – 1
– 6 – 1
– 5 – 1
– 4 – 1
HWBE 3 Hardware Boot Enable 0 (programmed) 1 (unprogrammed)
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)