ATtiny48 Atmel Corporation, ATtiny48 Datasheet - Page 176

• Manufacturer Part Number: ATtiny48
• Manufacturer: Atmel Corporation

Specifications of ATtiny48

• Flash (kbytes): 4 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 28
• Ext Interrupts: 28
• 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): 0.25
• Eeprom (bytes): 64
• 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: 2
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

17.13 Register Description
17.13.1
176
ATtiny48/88
ADMUX – ADC Multiplexer Selection Register
ADMUX register to “1000” enables the temperature sensor. The internal 1.1V voltage reference
must also be selected for the ADC voltage reference source in the temperature sensor measure-
ment. 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 17-2.
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.
• Bits 7, 4 – Res: Reserved Bits
These bits are reserved and will always read zero.
• Bit 6 – REFS0: Reference Selection Bit
This bit select the voltage reference for the ADC, as shown in
during a conversion, the change will not go in effect until this conversion is complete (ADIF in
ADCSRA is set).
Table 17-3.
Bit
(0x7C)
Read/Write
Initial Value
Temperature
ADC
REFS0
T = k * [(ADCH << 8) | ADCL] + T
0
1
Voltage Reference Selection
Internal 1.1V Voltage Reference
AV
Temperature vs. Sensor Output Voltage (Typical Case)
Voltage Reference Selections for ADC
CC
R
7
–
0
Reference
REFS0
R/W
6
0
Table 17-2
ADLAR
R/W
230 LSB
5
0
-40°C
are typical values. However, due to process variation the
R
0
4
–
OS
MUX3
R/W
3
0
MUX2
R/W
300 LSB
2
0
+25°C
Table
MUX1
R/W
1
0
17-3. If this bit is changed
MUX0
R/W
0
0
ADMUX
370 LSB
+85°C
8008H–AVR–04/11
Table 17-2
OS
10
is the
°C,