ADC Control and Status
Register A – ADCSRA
Bit
7
ADEN
R/W
0
6
ADSC
R/W
0
5
ADFR
R/W
0
4
ADIF
R/W
0
3
ADIE
R/W
0
2
ADPS2
R/W
0
1
ADPS1
R/W
0
0
ADPS0
R/W
0
ADCSRA
Read/Write
Initial Value
• Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turn-
ing 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 Run-
ning 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 initialization 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 – ADFR: ADC Free Running Select
When this bit is set (one) the ADC operates in Free Running mode. In this mode, the
ADC samples and updates the Data Registers continuously. Clearing this bit (zero) will
terminate Free Running mode.
• 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 dis-
abled. This also applies if the SBI and CBI instructions are used.
• Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Com-
plete Interrupt is activated.
204
ATmega8(L)
2486M–AVR–12/03
ATMEL [ ATMEL ]
