Datasheet
165
7701F–AVR–10/12
Atmel ATtiny24/44/84 [Preliminary]
Notes: 1. See “System Clock Prescaler” on page 31 for details.
2. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 7-7 on page 29 for details.
3. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8.0 MHz. See Table 7-6
on page 29 for details.
The status of the fuse bits is not affected by chip erase. Note that the fuse bits are locked if
lock bit 1 (LB1) is programmed. Program the fuse bits before programming the lock bits.
21.2.1 Latching of Fuses
The fuse values are latched when the device enters programming mode, and changes in 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.
21.3 Signature Bytes
All Atmel
®
microcontrollers have a three-byte signature code that 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 Atmel ATtiny24/44/84, the
signature bytes are given in Table 21-6.
21.4 Calibration Byte
The signature area of the Atmel ATtiny24/44/84 has one byte of calibration data for the inter-
nal RC oscillator. This byte resides in the high byte of address 0x000. During reset, this byte is
automatically written into the OSCCAL register to ensure the correct frequency of the cali-
brated RC oscillator.
Table 21-5. Fuse Low Byte
Fuse Low Byte Bit No Description Default Value
CKDIV8
(1)
7 Divide clock by 8 0 (programmed)
CKOUT 6 Clock Output Enable 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)
(2)
SUT0 4 Select start-up time 0 (programmed)
(2)
CKSEL3 3 Select Clock source 0 (programmed)
(3)
CKSEL2 2 Select Clock source 0 (programmed)
(3)
CKSEL1 1 Select Clock source 1 (unprogrammed)
(3)
CKSEL0 0 Select Clock source 0 (programmed)
(3)
Table 21-6. Device ID
Device
Signature Bytes Address
0x000 0x001 0x002
ATtiny24 0x1E 0x91 0x0B
ATtiny44 0x1E 0x92 0x07
ATtiny84 0x1E 0x93 0x0C