ATtiny24A Atmel Corporation, ATtiny24A Datasheet - Page 143

• Manufacturer Part Number: ATtiny24A
• Manufacturer: Atmel Corporation

Specifications of ATtiny24A

• Flash (kbytes): 2 Kbytes
• Pin Count: 14
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 4
• Hardware Qtouch Acquisition: No
• 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
• Eeprom (bytes): 128
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• 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: 4
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

16.11.3
16.12 Temperature Measurement
8183D–AVR–04/11
Bipolar Differential Conversion
If differential channels and a bipolar input mode are used, the result is
where V
and V
0x200 (-512d) through 0x1FF (+511d). The GAIN is either 1x or 20x. Note that if the user wants
to perform a quick polarity check of the result, it is sufficient to read the MSB of the result (ADC9
in ADCH). If the bit is one, the result is negative, and if this bit is zero, the result is positive.
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode
can be selected by writting the BIN bit in the ADCSRB to one. In the bipolar input mode two-
sided voltage differences are allowed and thus the voltage on the negative input pin can also be
larger than the voltage on the positive input pin.
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC8 channel. Selecting the ADC8 channel by writing the MUX[5:0] bits in
ADMUX register to “100010” enables the temperature sensor. 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 16-2.
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
T = k * [(ADCH << 8) | ADCL] + T
REF
POS
the selected voltage reference. The result is presented in two’s complement form, from
is the voltage on the positive input pin, V
Temperature vs. Sensor Output Voltage (Typical Case)
Table 16-2
ADC
230 LSB
-40
=
°
C
(
---------------------------------------------------- - GAIN
are typical values. However, due to process variation the
V
POS
OS
–
V
V
REF
NEG
) 512
⋅
NEG
300 LSB
+25
⋅
the voltage on the negative input pin,
ATtiny24A/44A/84A
°
C
370 LSB
+85
Table 16-2
°
C
OS
10
is the
143
°C,