Datasheet
182
ATmega323(L)
1457E–11/01
Fuse Bits The ATmega323 has 13 Fuse bits, divided in two groups. The Fuse High bits are
OCDEN, JTAGEN, SPIEN, EESAVE, BOOTSZ1..0, and BOOTRST, and the Fuse Low
bits are BODLEVEL, BODEN, and CKSEL3..0. All Fuses are accessible in parallel pro-
gramming mode and when programming via the JTAG interface. In serial programming
mode, all but the SPIEN Fuse is accessible.
• When the OCDEN fuse is programmed, the On-chip debug system is enabled if the
JTAGEN fuse is programmed. If the JTAGEN fuse is unprogrammed, the OCDEN
fuse has no visible effect.Never ship a product with the OCDEN fuse programmed.
Regardless of the setting of lockbits and the JTAGEN Fuse, a programmed OCDEN
fuse enables some parts of the clock system be running in all sleep modes. This
may increase the power consumption. Default value is unprogrammed (“1”).
• When the JTAGEN fuse is programmed, the JTAG interface is enabled on port C
pins PC5..2. Default value is programmed (“0”).
• When the SPIEN fuse is programmed (“0”), Serial Program and Data Downloading
are enabled. Default value is programmed (“0”). The SPIEN Fuse is not accessible
in SPI serial programming mode.
• When EESAVE is programmed, the EEPROM memory is preserved through the
Chip Erase cycle. Default value is unprogrammed (“1”). The EESAVE Fuse bit can
not be programmed if any of the Lock bits are programmed.
• BOOTSZ1..0 select the size and start address of the Boot Flash section according
to Table on page 172. Default value is “11” (both unprogrammed).
• When BOOTRST is programmed (“0”), the reset vector is set to the start address of
the Boot Flash section, as selected by the BOOTSZ fuses according to Table on
page 172. If the BOOTRST is unprogrammed (“1”), the reset vector is set to address
$0000. Default value is unprogrammed (“1”).
• The BODLEVEL Fuse selects the Brown-out Detection Level and changes the Start-
up times, according to Table 5 on page 26 and Table 6 on page 27, respectively.
Default value is unprogrammed (“1”).
• When the BODEN Fuse is programmed (“0”), the Brown- out Detector is enabled.
See “Reset and Interrupt Handling” on page 22. Default value is unprogrammed
(“1”).
• CKSEL3..0 select the clock source and the start-up delay after reset, according to
Table 1 on page 6 and Table 6 on page 27. Default value is “0010” (Internal RC
Oscillator, slowly rising power).
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.
Signature Bytes All Atmel microcontrollers have a three-byte signature code which identifies the device.
This code can be read in both serial and parallel mode. The three bytes reside in a sep-
arate address space.
For the ATmega323 the signature bytes are:
1. $000: $1E (indicates manufactured by Atmel)
2. $001: $95 (indicates 32KB Flash memory)
3. $002: $01 (indicates ATmega323 device when $001 is $95)