Datasheet

WDTCSR on page 75

System and Reset Characteristics on page 399

Clock characteristics on page 398

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 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 device the signature bytes are given in the following table.

Table 28-9. Device and JTAG ID

Part Signature Bytes Address JTAG

0x000 0x001 0x002 Part number Manufacture ID

ATmega644A 0x1E 0x96 0x09 960A 0x1F

28.4. Calibration Byte

The device 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 calibrated RC Oscillator.