Datasheet

27
2586D–AVR–02/06
ATtiny25/45/85
ing a 4x multiplied frequency from the reference clock. The resulting frequency is 25.6 MHz and
it is needed for supporting the same PWM frequencies as in ATtiny15.
Note: 1. The device is shipped with this option selected.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-7 and the start-up times in ATtiny15 compatibility mode in Table 7-8..
Note: 1. The device is shipped with this option selected.
7.6.1 OSCCAL – Oscillator Calibration Register
• Bits 7:0 – CAL7:0: Oscillator Calibration Value
Writing the calibration byte to this address will trim the internal Oscillator to remove process vari-
ations from the Oscillator frequency. This is done automatically during Chip Reset. When
OSCCAL is zero, the lowest available frequency is chosen. Writing non-zero values to this regis-
ter will increase the frequency of the internal Oscillator. Writing 0xFF to the register gives the
highest available frequency. The calibrated Oscillator is used to time EEPROM and Flash
access. If EEPROM or Flash is written, do not calibrate to more than 8.8 MHz frequency. Other-
wise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two fre-
Table 7-6. Internal Calibrated RC Oscillator Operating Modes
CKSEL3:0 Nominal Frequency
0010
(1)
8.0 MHz
0011 6.4 MHz
Table 7-7. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1:0
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 6 CK 14CK BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10
(1)
6 CK 14CK + 64 ms Slowly rising power
11 Reserved
Table 7-8. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1:0
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 6 CK 14CK + 64 ms
01 6 CK 14CK + 64 ms
10
(1)
6 CK 14CK + 4 ms
11 1 CK 14CK
Bit 76543210
0x31 CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 Device Specific Calibration Value