1 latching of fuses, 4 signature bytes, 5 calibration byte – Rainbow Electronics ATmega64M1 User Manual
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293
8209A–AVR–08/09
ATmega16M1/32M1/64M1
Notes:
1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See
for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See
for details.
3. The CKOUT Fuse allows the system clock to be output on PORTB0. See
for details.
4. See
“System Clock Prescaler” on page 34
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.
28.3.1
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.
28.4
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. For the ATmega16M1/32M1/64M1 the signature
bytes are given in
.
28.5
Calibration Byte
The ATmega16M1/32M1/64M1 has a byte calibration value for the internal RC Oscillator. This
byte resides in the high byte of address 0x000 in the signature address space. During reset, this
byte is automatically written into the OSCCAL Register to ensure correct frequency of the cali-
brated RC Oscillator.
Table 28-8.
Signature Bytes
Part
Signature Bytes Address
0x000
0x001
0x002
ATmega16M1
0x1E
0x94
0x84
ATmega32M1
0x1E
0x95
0x84
ATmega64M1
0x1E
0x95
0x84