atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 241

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

18.8.1
18.8.2
18.9
18.9.1
7647A–AVR–02/08
ADC Register Description
User Calibration
Manufacturing Calibration
ADC Multiplexer Register – ADMUX
The measured voltage has a linear relationship to the temperature as described in
page
measurement is +/- 10° C after bandgap calibration.
Table 18-3.
The values described in
variation the 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 appli-
cation software.
The software calibration requires that a calibration value is measured and stored in a register or
EEPROM for each chip. The software calibration can be done utilizing the formula:
where ADCH & ADCL are the ADC data registers, k is a fixed coefficient and T
ature sensor offset value determined and stored into EEPROM.
One can also use the calibration values available in the signature row
ture Row from Software” on page 283.
The calibration values are determined from values measured during test at room temperature
which is approximatively +25°C and during test at hot temperature which is approximatively
+125°C.
The temperature in Celsius degrees can be calculated utilizing the formula:
Where:
The ADC of the ATmega32/64/M1/C1 is controlled through 3 different registers. The ADCSRA
and The ADCSRB registers which are the ADC Control and Status registers, and the ADMUX
which allows to select the Vref source and the channel to be converted.
The conversion result is stored on ADCH and ADCL register which contain respectively the most
significant bits and the less significant bits.
Bit
Temperature / °C
241. The voltage sensitivity is approximately 1 mV/
a. ADCH & ADCL are the ADC data registers,
b. TSGAIN is the temperature sensor gain (constant 1, or unsigned fixed point num-
c. TSOFFSET is the temperature sensor offset correction term (2. complement
Voltage / mV
ber, 0x80 = decimal 1.0)
signed byte)
Temperature vs. Sensor Output Voltage (Typical Case)
REFS1
7
T = { [ (ADCH << 8) | ADCL ] *TSGAIN } +TSOFFSET-273
Table 18-3 on page 241
REFS0
6
T = { [ (ADCH << 8) | ADCL ] - T
600 mV
-40 °C
ADLAR
5
MUX4
4
are typical values. However, due to the process
MUX3
3
°
ATmega32/64/M1/C1
762 mv
C and the accuracy of the temperature
+25 °C
OS
MUX2
2
} / k
MUX1
See “Reading the Signa-
1
MUX0
OS
0
1012 mV
+125 °C
Table 18-3 on
is the temper-
ADMUX
241