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Rev. 1.00, 05/04, page 419 of 544
16.4 Operation
The A/D converter operates by successive approximation with 10-bit resolution. It has two
operating modes: single mode and scan mode. When changing the operating mode or analog input
channel, to prevent incorrect operation, first clear the ADST bit to 0 in ADCSR to halt A/D
conversion. The ADST bit can be set at the same time as the operating mode or analog input
channel is changed.
16.4.1 Single Mode
In single mode, A/D conversion is to be performed only once on the specified single channel.
Operations are as follows.
1. A/D conversion on the specified channel is started when the ADST bit in ADCSR is set to 1,
by software or an external trigger input.
2. When A/D conversion is completed, the result is transferred to the A/D data register
corresponding to the channel.
3. On completion of A/D conversion, the ADF bit in ADCSR is set to 1. If the ADIE bit is set to
1 at this time, an ADI interrupt request is generated.
4. The ADST bit remains set to 1 during A/D conversion. When conversion ends, the ADST bit is
automatically cleared to 0, and the A/D converter enters wait state.
16.4.2 Scan Mode
Scan mode is useful for monitoring analog inputs in a group of one or more channels. When the
ADST bit is set to 1 by software, or by timer or external trigger input, A/D conversion starts on the
first channel in the group (AN0 when CH2 = 0; AN4 when CH2 = 1).
When two or more channels are selected, after conversion of the first channel ends, conversion of
the second channel (AN1 or AN5) starts immediately. A/D conversion continues cyclically on the
selected channels until the ADST bit is cleared to 0. The conversion results are transferred for
storage into the ADDR registers corresponding to the channels.
Typical operations when three channels (AN0 to AN2) are selected in scan mode are described
below.