ATtiny85 Atmel Corporation, ATtiny85 Datasheet - Page 32

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ATtiny85

Manufacturer Part Number
ATtiny85
Description
Manufacturer
Atmel Corporation
Datasheets

Specifications of ATtiny85

Flash (kbytes)
8 Kbytes
Pin Count
8
Max. Operating Frequency
20 MHz
Cpu
8-bit AVR
# Of Touch Channels
3
Hardware Qtouch Acquisition
No
Max I/o Pins
6
Ext Interrupts
6
Usb Speed
No
Usb Interface
No
Spi
1
Twi (i2c)
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
4
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Resistive Touch Screen
No
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
0.5
Eeprom (bytes)
512
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
No
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8 to 5.5
Operating Voltage (vcc)
1.8 to 5.5
Fpu
No
Mpu / Mmu
no / no
Timers
2
Output Compare Channels
5
Pwm Channels
6
32khz Rtc
No
Calibrated Rc Oscillator
Yes

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6.4
6.5
6.5.1
32
Clock Output Buffer
Register Description
ATtiny25/45/85
OSCCAL – Oscillator Calibration Register
The device can output the system clock on the CLKO pin (when not used as XTAL2 pin). To
enable the output, the CKOUT Fuse has to be programmed. This mode is suitable when the chip
clock is used to drive other circuits on the system. Note that the clock will not be output during
reset and that the normal operation of the I/O pin will be overridden when the fuse is pro-
grammed. Internal RC Oscillator, WDT Oscillator, PLL, and external clock (CLKI) can be
selected when the clock is output on CLKO. Crystal oscillators (XTAL1, XTAL2) can not be used
for clock output on CLKO. If the System Clock Prescaler is used, it is the divided system clock
that is output.
• Bits 7:0 – CAL[7:0]: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. A pre-programmed calibration value is
automatically written to this register during chip reset, giving the Factory calibrated frequency as
specified in
the oscillator frequency. The oscillator can be calibrated to frequencies as specified in
2 on page
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, 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-
quency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL[6:0] bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the
range.
To ensure stable operation of the MCU the calibration value should be changed in small. A vari-
ation in frequency of more than 2% from one cycle to the next can lead to unpredicatble
behavior. Changes in OSCCAL should not exceed 0x20 for each calibration. It is required to
ensure that the MCU is kept in Reset during such changes in the clock frequency
Table 6-14.
Bit
0x31
Read/Write
Initial Value
OSCCAL Value
0x3F
0x7F
0x00
169. Calibration outside that range is not guaranteed.
Table 21-2 on page
Internal RC Oscillator Frequency Range
CAL7
R/W
7
with Respect to Nominal Frequency
CAL6
Typical Lowest Frequency
R/W
6
169. The application software can write this register to change
CAL5
R/W
100%
5
50%
75%
Device Specific Calibration Value
CAL4
R/W
4
CAL3
R/W
3
with Respect to Nominal Frequency
CAL2
R/W
2
Typical Highest Frequency
CAL1
R/W
1
100%
150%
200%
CAL0
R/W
0
2586N–AVR–04/11
Table 21-
OSCCAL

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