ATtiny20 Atmel Corporation, ATtiny20 Datasheet - Page 123

• Manufacturer Part Number: ATtiny20
• Manufacturer: Atmel Corporation

Specifications of ATtiny20

• Flash (kbytes): 2 Kbytes
• Pin Count: 14
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 5
• Hardware Qtouch Acquisition: Yes
• Max I/o Pins: 12
• Ext Interrupts: 12
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 0.12
• Self Program Memory: NO
• 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: 4
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

15.11 ADC Conversion Result
15.12 Temperature Measurement
8235B–AVR–04/11
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Data Registers (ADCL, ADCH). The result is, as follows:
where V
Table 15-3 on page 124
0x3FF represents the selected reference voltage minus one LSB. The result is presented in one-
sided form, from 0x3FF to 0x000.
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC channel. The temperature sensor is measured via channel ADC8 and is
enabled by writing MUX bits in ADMUX register to “1010”. The internal 1.1V reference must also
be selected for the ADC reference source in the temperature sensor measurement. When the
temperature sensor is enabled, the ADC converter can be used in single conversion mode to
measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in
The sensitivity is approximately 1 LSB / °C and the accuracy depends on the method of user cal-
ibration. Typically, the measurement accuracy after a single temperature calibration is ±
assuming calibration at room temperature. Better accuracies are achieved by using two
temperature points for calibration.
Table 15-2.
The values described in
temperature sensor output voltage varies from one chip to another. To be capable of achieving
more accurate results the temperature measurement can be calibrated in the application soft-
ware. The sofware calibration can be done using the formula:
where ADCH and ADCL are the ADC data registers, k is the fixed slope coefficient and T
temperature sensor offset. Typically, k is very close to 1.0 and in single-point calibration the
coefficient may be omitted. Where higher accuracy is required the slope coefficient should be
evaluated based on measurements at two temperatures.
Temperature
ADC
• Quantization Error: Due to the quantization of the input voltage into a finite number of codes,
• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to
a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
an ideal transition for any code. This is the compound effect of offset, gain error, differential
error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
T = k * [(ADCH << 8) | ADCL] + T
IN
is the voltage on the selected input pin and V
Temperature vs. Sensor Output Voltage (Typical Case)
Table 15-2
and
Table 15-4 on page
230 LSB
-40°C
are typical values. However, due to process variation the
ADC
OS
=
V
--------------------------
IN
V
⋅
REF
1024
124). 0x000 represents analog ground, and
REF
300 LSB
+25°C
the selected voltage reference (see
ATtiny20
370 LSB
+85°C
Table 15-2
OS
10
is the
123
°C,