92
2535J–AVR–08/10
ATtiny13
Bits 4:2 – Res: Reserved Bits
These bits are reserved bits in the ATtiny13 and will always read as zero.
Bits 1:0 – MUX1:0: Analog Channel Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC.
will not go in effect until this conversion is complete (ADIF in ADCSRA is set).
14.12.2
ADCSRA – ADC Control and Status Register A
Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning the
ADC off while a conversion is in progress, will terminate this conversion.
Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mode, write this bit to one to start each conversion. In Free Running mode,
write this bit to one to start the first conversion. The first conversion after ADSC has been written
after the ADC has been enabled, or if ADSC is written at the same time as the ADC is enabled,
will take 25 ADC clock cycles instead of the normal 13. This first conversion performs initializa-
tion of the ADC.
ADSC will read as one as long as a conversion is in progress. When the conversion is complete,
it returns to zero. Writing zero to this bit has no effect.
Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a con-
version on a positive edge of the selected trigger signal. The trigger source is selected by setting
the ADC Trigger Select bits, ADTS in ADCSRB.
Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the data registers are updated. The ADC
Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF is
cleared by hardware when executing the corresponding interrupt handling vector. Alternatively,
ADIF is cleared by writing a logical one to the flag. Beware that if doing a Read-Modify-Write on
ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and CBI instructions
are used.
Table 14-3.
Input Channel Selections
MUX1..0
Single Ended Input
00
ADC0 (PB5)
01
ADC1 (PB2)
10
ADC2 (PB4)
11
ADC3 (PB3)
Bit
76543210
ADEN
ADSC
ADATE
ADIF
ADIE
ADPS2
ADPS1
ADPS0
ADCSRA
Read/Write
R/W
Initial Value
00000000