300
7647H–AVR–03/12
Atmel ATmega16/32/64/M1/C1
Notes: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 5-9 on page 37 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator at 8MHz. See Table 5-9 on
page 37 for details.
3. The CKOUT Fuse allows the system clock to be output on PORTB0. See “Clock Output Buffer”
on page 37 for details.
4. See “System Clock Prescaler” on page 37 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.
25.3.1 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.
25.4 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, also when the device is locked. The three
bytes reside in a separate address space.
25.4.1 Signature Bytes
For the ATmega16M1 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x94 (indicates 16KB Flash memory).
3. 0x002: 0x84 (indicates ATmega16M1 device when 0x001 is 0x94).
For the ATmega32M1 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x95 (indicates 32KB Flash memory).
3. 0x002: 0x84 (indicates ATmega32M1 device when 0x001 is 0x95).
Table 25-7. Fuse Low Byte
Low Fuse Byte Bit No Description Default Value
CKDIV8
(4)
7 Divide clock by 8 0 (programmed)
CKOUT
(3)
6 Clock output 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)
(1)
SUT0 4 Select start-up time 0 (programmed)
(1)
CKSEL3 3 Select Clock source 0 (programmed)
(2)
CKSEL2 2 Select Clock source 0 (programmed)
(2)
CKSEL1 1 Select Clock source 1 (unprogrammed)
(2)
CKSEL0 0 Select Clock source 0 (programmed)
(2)
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