ATtiny26 Atmel Corporation, ATtiny26 Datasheet - Page 97

• Manufacturer Part Number: ATtiny26
• Manufacturer: Atmel Corporation

Specifications of ATtiny26

• Flash (kbytes): 2 Kbytes
• Pin Count: 20
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 16
• Ext Interrupts: 11
• 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: No
• Crypto Engine: No
• Sram (kbytes): 0.12
• Eeprom (bytes): 128
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 3
• Pwm Channels: 4
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

1477K–AVR–08/10
The ADC module contains a prescaler, which divides the system clock to an acceptable ADC
clock frequency.
The ADPS bits in ADCSR are used to generate a proper ADC clock input frequency from any
chip clock frequency above 100 kHz. The prescaler starts counting from the moment the ADC is
switched on by setting the ADEN bit in ADCSR. The prescaler keeps running for as long as the
ADEN bit is set, and is continuously reset when ADEN is low.
When initiating a conversion by setting the ADSC bit in ADCSR, the conversion starts at the fol-
lowing rising edge of the ADC clock cycle. If differential channels are selected, the conversion
will only start at every other rising edge of the ADC clock cycle after ADEN was set.
A normal conversion takes 13 ADC clock cycles. In certain situations, the ADC needs more
clock cycles to initialization and minimize offset errors. Extended conversions take 25 ADC clock
cycles and occur as the first conversion after the ADC is switched on (ADEN in ADCSR is set).
Special care should be taken when changing differential channels. Once a differential channel
has been selected, the gain stage may take as much as 125 µs to stabilize to the new value.
Thus conversions should not be started within the first 125 µs after selecting a new differential
channel. Alternatively, conversions results obtained within this period should be discarded. The
same settling time should be observed for the first differential conversion after changing ADC
reference (by changing the REFS1:0 bits in ADMUX).
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conver-
sion and 13.5 ADC clock cycles after the start of an extended conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In Single Conversion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge. In Free Running mode, a new con-
version will be started immediately after the conversion completes, while ADSC remains high.
Using Free Running mode and an ADC clock frequency of 200 kHz gives the lowest conversion
time, 65
Figure 53. ADC Timing Diagram, Extended Conversion (Single Conversion Mode)
Cycle Number
ADC Clock
ADEN
ADSC
ADIF
ADCH
ADCL
µs
, equivalent to 15 kSPS. For a summary of conversion times, see Table 43.
1
2
MUX and REFS
Update
12
13
14
15
Sample & Hold
16
Extended Conversion
17
18
19
20
21
22
Conversion
Complete
23
24
25
MSB of Result
LSB of Result
Next
Conversion
1
2
MUX and REFS
Update
3
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