ATTINY25-20SUR Atmel, ATTINY25-20SUR Datasheet - Page 138

• Manufacturer Part Number: ATTINY25-20SUR
• Description: MCU AVR 2KB FLASH 20MHZ 8SOIC
• Manufacturer: Atmel
• Series: AVR® ATtinyr

Specifications of ATTINY25-20SUR

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: USI
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 6
• Program Memory Size: 2KB (1K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 128 x 8
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 4x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

17.13 Register Description
17.13.1
138
ATtiny25/45/85
ADMUX – ADC Multiplexer Selection Register
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
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, 4 – REFS[2:0]: Voltage Reference Selection Bits
These bits select the voltage reference (V
are changed during a conversion, the change will not go in effect until this conversion is
complete (ADIF in ADCSR is set). Whenever these bits are changed, the next conversion will
take 25 ADC clock cycles. When differential channels and gain are used, using V
external AREF higher than (V
affect the ADC accuracy.
Table 17-3.
Note:
Bit
0x07
Read/Write
Initial Value
Temperature
ADC
REFS2
T = k * [(ADCH << 8) | ADCL] + T
X
X
0
0
1
1
1. The device requries a supply voltage of 3V in order to generate 2.56V reference voltage.
REFS1
Temperature vs. Sensor Output Voltage (Typical Case)
Voltage Reference Selections for ADC
REFS1
0
0
1
1
1
1
R/W
7
0
REFS0
REFS0
Table 17-2
R/W
6
0
0
1
0
1
0
1
CC
230 LSB
-40
ADLAR
- 1V) as a voltage reference is not recommended as this will
R/W
V
External Voltage Reference at PB0 (AREF) pin, Internal Voltage
Reference turned off.
Internal 1.1V Voltage Reference.
Reserved
Internal 2.56V Voltage Reference without external bypass
capacitor, disconnected from PB0 (AREF)
Internal 2.56V Voltage Reference with external bypass capacitor at
PB0 (AREF) pin
Voltage Reference (V
5
0
°
CC
C
are typical values. However, due to process variation the
used as Voltage Reference, disconnected from PB0 (AREF).
REF
REFS2
OS
R/W
4
0
) for the ADC, as shown in
(1)
.
MUX3
R/W
3
0
REF
300 LSB
+25
) Selection
MUX2
°
R/W
C
2
0
MUX1
R/W
1
0
Table
(1)
.
17-3. If these bits
MUX0
R/W
0
0
370 LSB
2586M–AVR–07/10
+85
°
C
CC
ADMUX
or an
OS
is