ATtiny261 Atmel Corporation, ATtiny261 Datasheet - Page 155

• Manufacturer Part Number: ATtiny261
• Manufacturer: Atmel Corporation

Specifications of ATtiny261

• Flash (kbytes): 2 Kbytes
• Pin Count: 20
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 4
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 16
• Ext Interrupts: 16
• 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: Yes
• Crypto Engine: No
• Sram (kbytes): 0.12
• Eeprom (bytes): 128
• 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: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

15.13 Register Description
15.13.1
2588E–AVR–08/10
ADMUX – ADC Multiplexer Selection Register
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
the 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.
• Bits 7:6 – REFS1:REFS0: Voltage Reference Selection Bits
These bits together with the REFS2 bit from the ADC Control and Status Register B (ADCSRB)
select the voltage reference for the ADC, as shown in
Table 15-3.
If these bits are changed during a conversion, the change will not go in effect until this conver-
sion is complete (ADIF in ADCSR is set). Also note, that when these bits are changed, the next
conversion will take 25 ADC clock cycles.
Bit
0x07 (0x27)
Read/Write
Initial Value
Temperature
ADC
T = k * [(ADCH << 8) | ADCL] + T
REFS2
X
X
0
0
1
1
Temperature vs. Sensor Output Voltage (Typical Case)
Voltage Reference Selections for ADC
REFS1
R/W
7
0
REFS1
0
0
1
1
1
1
REFS0
Table 15-2
R/W
6
0
230 LSB
-40 °C
ADLAR
REFS0
R/W
5
0
0
1
0
1
0
1
are typical values. However, due to process variation the
MUX4
OS
R/W
4
0
Voltage Reference Selection
V
disconnected from AREF
External voltage reference at AREF pin,
internal voltage reference turned off
Internal 1.1V voltage reference
Reserved
Internal 2.56V voltage reference,
without external bypass capacitor,
disconnected from AREF
Internal 2.56V voltage reference,
with external bypass capacitor at AREF pin
CC
used as voltage reference,
MUX3
R/W
3
0
Table
300 LSB
+25 °C
15-3.
MUX2
R/W
2
0
MUX1
R/W
1
0
MUX0
R/W
0
0
370 LSB
+85 °C
ADMUX
OS
155
is