Datasheet

Fuse Low Byte Bit No. Description Default Value

CKSEL1 1 Select Clock source 0 (programmed)

(2)

CKSEL0 0 Select Clock source 1 (unprogrammed)

(2)

Note:

1. The default value of SUT1:0 results in maximum start-up time. See table Start-up Times for the

Internal Calibrated RC Oscillator Clock Selection in section Calibrated Internal RC Oscillator for

details.

2. The default setting of CKSEL3:0 results in Internal RC Oscillator @ 1MHz. See table Device

Clocking Options Select in section Clock Sources 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.

Related Links

ATmega64A Boot Loader Parameters on page 379

Calibrated Internal RC Oscillator on page 56

ATmega103 and ATmega64A Compatibility on page 13

Clock Sources on page 53

31.2.1. 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.

31.3. 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 ATmega64A the signature bytes are given in the following table.

Table 31-6 Device and JTAG ID

Part Signature Bytes Address JTAG

0x000 0x001 0x002 Part Number Manufacture ID

ATmega64A 0x1E 0x96 0x02 9602 0x1F

31.4. Calibration Byte

The ATmega64A stores four different calibration values for the internal RC Oscillator. These bytes resides

in the signature row High byte of the addresses 0x0000, 0x0001, 0x0002, and 0x0003 for 1, 2, 4, and

8MHz respectively. During Reset, the 1MHz value is automatically loaded into the OSCCAL Register. If

other frequencies are used, the calibration value has to be loaded manually, see OSCCAL – Oscillator

Calibration Register for details.