
276
ATmega64A [DATASHEET]
8160D–AVR–02/2013
Note:
1. The SPIEN Fuse is not accessible in SPI Serial Programming mode.
2. The CKOPT Fuse functionality depends on the setting of the CKSEL bits. See
details.
4. If the JTAG interface is left unconnected, the JTAGEN fuse should if possible be disabled. This to avoid static cur-
rent at the TDO pin in the JTAG interface
Note:
1. The default value of SUT1:0 results in maximum start-up time. See
Table 9-8 on page 39 for details.
2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 1 MHz. See
Table 9-1 on page 35 for details.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if Lock bit1 (LB1) is
programmed. Program the Fuse bits before programming the Lock bits.
28.2.1
Latching of Fuses
The fuse values are latched when the device enters Programming mode and changes of the fuse values will have
no effect until the part leaves Programming mode. This does not apply to the EESAVE Fuse which will take effect
once it is programmed. The fuses are also latched on Power-up in Normal mode.
28.3
Signature Bytes
All Atmel microcontrollers have a 3-byte signature code which identifies the device. This code can be read in both
Serial and Parallel mode, also when the device is locked. The three bytes reside in a separate address space.
For the ATmega64A the signature bytes are:
Table 28-4.
Fuse High Byte
Fuse High Byte
Bit no
Description
Default Value
OCDEN
7
Enable OCD
1 (unprogrammed, OCD disabled)
6
Enable JTAG
0 (programmed, JTAG enabled)
5
Enable SPI Serial Program and Data
Downloading
0 (programmed, SPI prog. enabled)
4
Oscillator options
1 (unprogrammed)
EESAVE
3
EEPROM memory is preserved through the Chip
Erase
1 (unprogrammed, EEPROM not
preserved)
BOOTSZ1
2
BOOTSZ0
1
BOOTRST
0
Select Reset Vector
1 (unprogrammed)
Table 28-5.
Fuse Low Byte
Fuse Low Byte
Bit no
Description
Default Value
BODLEVEL
7
Brown out detector trigger level
1 (unprogrammed)
BODEN
6
Brown out detector enable
1 (unprogrammed, BOD disabled)
SUT1
5
Select start-up time
SUT0
4
Select start-up time
CKSEL3
3
Select Clock source
CKSEL2
2
Select Clock source
CKSEL1
1
Select Clock source
CKSEL0
0
Select Clock source