ATTINY261A-XUR Atmel, ATTINY261A-XUR Datasheet - Page 146

• Manufacturer Part Number: ATTINY261A-XUR
• Description: MCU AVR 2KB FLASH 20MHZ 20TSSOP
• Manufacturer: Atmel
• Series: AVR® ATtinyr

Specifications of ATTINY261A-XUR

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: USI
• Peripherals: Brown-out Detect/Reset, POR, PWM, Temp Sensor, WDT
• Number Of I /o: 16
• 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): 1.8 V ~ 5.5 V
• Data Converters: A/D 11x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

15.6
15.6.1
146
Changing Channel or Reference Selection
ATtiny261A/461A/861A
ADC Input Channels
For a summary of conversion times, see
Table 15-1.
The MUX5:0 and REFS2:0 bits in the ADCSRB and ADMUX registers are single buffered
through a temporary register to which the CPU has random access. This ensures that the chan-
nels and reference selection only takes place at a safe point during the conversion. The channel
and reference selection is continuously updated until a conversion is started. Once the conver-
sion starts, the channel and reference selection is locked to ensure a sufficient sampling time for
the ADC. Continuous updating resumes in the last ADC clock cycle before the conversion com-
pletes (ADIF in ADCSRA is set). Note that the conversion starts on the following rising ADC
clock edge after ADSC is written. The user is thus advised not to write new channel or reference
selection values to ADMUX until one ADC clock cycle after ADSC is written.
If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX Register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings.
ADMUX can be safely updated in the following ways:
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the channel before starting the conversion. The chan-
nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the conversion to complete before changing the channel selection.
In Free Running mode, always select the channel before starting the first conversion. The chan-
nel selection may be changed one ADC clock cycle after writing one to ADSC. However, the
simplest method is to wait for the first conversion to complete, and then change the channel
Condition
First conversion
Normal conversions
Auto Triggered conversions
• When ADATE or ADEN is cleared.
• During conversion, minimum one ADC clock cycle after the trigger event.
• After a conversion, before the Interrupt Flag used as trigger source is cleared.
ADC Conversion Time
Sample & Hold
(Cycles from Start of Conversion)
Table
13.5
1.5
2
15-1.
Total Conversion Time (Cycles)
13.5
25
13
8197B–AVR–01/10