ATtiny26 Atmel Corporation, ATtiny26 Datasheet - Page 29

• Manufacturer Part Number: ATtiny26
• Manufacturer: Atmel Corporation

Specifications of ATtiny26

• Flash (kbytes): 2 Kbytes
• Pin Count: 20
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 16
• Ext Interrupts: 11
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 11
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 0.12
• Eeprom (bytes): 128
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 3
• Pwm Channels: 4
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

Calibrated Internal
RC Oscillator
Oscillator Calibration
Register – OSCCAL
1477K–AVR–08/10
The calibrated internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All frequen-
cies are nominal values at 5V and 25°C. This clock may be selected as the system clock by pro-
gramming the CKSEL Fuses as shown in Table 11. If selected, it will operate with no external
components. The CKOPT Fuse should always be unprogrammed when using this clock option.
During Reset, hardware loads the calibration byte into the OSCCAL Register and thereby auto-
matically calibrates the RC Oscillator. At 5V, 25°C and 1.0 MHz Oscillator frequency selected,
this calibration gives a fre-quency within ± 3% of the nominal frequency. Using run-time calibra-
tion methods as described in application notes available at www.atmel.com/avr it is possible to
achieve ± 1% accuracy at any given V
chip clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the reset
time-out. For more information on the pre-programmed calibration value, see the section “Cali-
bration Byte” on page 109.
Table 11. Internal Calibrated RC Oscillator Operating Modes
Note:
When this oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 12. PB4 (XTAL1) and PB5 (XTAL2) can be used as general I/O ports.
Table 12. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
Note:
• 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. During Reset, the 1 MHz calibration value which is located
in the signature row high byte (address 0x00) is automatically loaded into the OSCCAL Register.
If the internal RC is used at other frequencies, the calibration value must be loaded manually.
This can be done by first reading the signature row by a programmer, and then store the calibra-
tion values in the Flash or EEPROM. Then the value can be read by software and loaded into
the OSCCAl Register. When OSCCAL is zero, the lowest available frequency is chosen. Writing
non-zero values to this register will increase the frequency of the internal oscillator. Writing $FF
to the register gives the highest available frequency. The calibrated Oscillator is used to time
SUT1..0
10
00
01
11
(1)
Bit
$31 ($51)
Read/Write
Initial Value
1. The device is shipped with this option selected.
1. The device is shipped with this option selected.
CKSEL3..0
Start-up Time from
0001
0010
0100
0011
Power-down
(1)
CAL7
R/W
6 CK
6 CK
6 CK
7
CAL6
R/W
6
CAL5
R/W
Additional Delay from
5
Device Specific Calibration Value
Reset (V
CC
and Temperature. When this oscillator is used as the
CAL4
R/W
4.1 ms
65 ms
4
Reserved
CC
–
Nominal Frequency (MHz)
= 5.0V)
CAL3
R/W
3
1.0
2.0
4.0
8.0
CAL2
R/W
2
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
CAL1
R/W
1
CAL0
R/W
0
OSCCAL
29