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Section 14 A/D Converter (8 Analog Input Channel Version)
14.4 Operation
The A/D converter operates by successive approximations with 10-bit resolution. It has two
operating modes: single mode and scan mode.
14.4.1 Single Mode (SCAN = 0)
Single mode is selected when A/D conversion is to be performed on a single channel only. A/D
conversion is started when the ADST bit is set to 1 by software or by external trigger input. The
ADST bit remains set to 1 during A/D conversion, and is automatically cleared to 0 when
conversion ends.
On completion of conversion, the ADF flag is set to 1. If the ADIE bit is set to 1 at this time, an
ADI interrupt request is generated. The ADF flag is cleared by writing 0 to it after reading
ADCSR.
When the operating mode or analog input channel must be changed during analog conversion, to
prevent incorrect operation, first clear the ADST bit to 0 in ADCSR to halt A/D conversion. After
making the necessary changes, set the ADST bit to 1 to start A/D conversion again. The ADST
bit can be set at the same time as the operating mode or input channel is changed.
Typical operations when channel 1 (AN1) is selected in single mode are described next. Figure
14.3 shows a timing diagram for this example.
[1] Single mode is selected (SCAN = 0), input channel AN1 is selected (CH2 = 0, CH1 = 0,
CH0 = 1), the A/D interrupt is enabled (ADIE = 1), and A/D conversion is started (ADST = 1).
[2] When A/D conversion is completed, the result is transferred to ADDRB. At the same time the
ADF flag is set to 1, the ADST bit is cleared to 0, and the A/D converter becomes idle.
[3] Since ADF = 1 and ADIE = 1, an ADI interrupt is requested.
[4] The A/D interrupt handling routine starts.
[5] The routine reads ADCSR, then writes 0 to the ADF flag.
[6] The routine reads and processes the conversion result (ADDRB).
[7] Execution of the A/D interrupt handling routine ends. After that, if the ADST bit is set to 1,
A/D conversion starts again and steps [2] to [7] are repeated.
Rev.7.00 Feb. 14, 2007 page 541 of 1108
REJ09B0089-0700