Note that fuse bits are locked if Lock Bit 1 (LB1) is programmed. Program the fuse bits before programming the lock bits. The status of the fuse bits is not affected by Chip Erase.

Fuse bits can also be read by the device firmware. See section “Reading Fuse and Lock Bits from Firmware” on page 99.

17.2.1Latching 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.

17.3Calibration Bytes

The signature area of the ATtiny13 contains two bytes of calibration data for the internal oscillator. The calibration data in the high byte of address 0x00 is for use with the oscillator set to 9.6 MHz operation. During reset, this byte is automatically written into the OSCCAL register to ensure correct frequency of the oscillator.

There is a separate calibration byte for the internal oscillator in 4.8 MHz mode of operation but this data is not loaded automatically. The hardware always loads the 9.6 MHz calibraiton data during reset. To use separate calibration data for the oscillator in 4.8 MHz mode the OSCCAL register must be updated by firmware. The calibration data for 4.8 MHz operation is located in the high byte at address 0x01 of the signature area.

17.4Signature Bytes

All Atmel microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial and high-voltage programming mode, even when the device is locked. The three bytes reside in a separate address space.

For the ATtiny13 the signature bytes are:

•0x000: 0x1E (indicates manufactured by Atmel).

•0x001: 0x90 (indicates 1 KB Flash memory).

•0x002: 0x07 (indicates ATtiny13 device when 0x001 is 0x90).

17.5Page Size

104 ATtiny13

2535J–AVR–08/10