H8SLASH3021 datasheet(455/712 Pages) RENESAS

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13. A/D Converter

Rev.2.00 Mar. 22, 2007 Page 431 of 684

REJ09B0352-0200

13.4.2

Scan Mode (SCAN = 1)

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 external trigger input, A/D conversion starts on the first

channel in the group (AN

0 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 (AN

1 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 A/D data registers

corresponding to the channels.

When the mode or analog input channel selection 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. A/D conversion will start again from the

first channel in the group. The ADST bit can be set at the same time as the mode or channel

selection is changed.

Typical operations when three channels in group 0 (AN

0 to AN2) are selected in scan mode are

described next. Figure 13.4 shows a timing diagram for this example.

1. Scan mode is selected (SCAN = 1), scan group 0 is selected (CH2 = 0), analog input channels

0 to AN2 are selected (CH1 = 1, CH0 = 0), and A/D conversion is started (ADST = 1).

2. When A/D conversion of the first channel (AN

0) is completed, the result is transferred into

ADDRA. Next, conversion of the second channel (AN

1) starts automatically.

3. Conversion proceeds in the same way through the third channel (AN

2).

4. When conversion of all selected channels (AN

0 to AN2) is completed, the ADF flag is set to 1

and conversion of the first channel (AN

0) starts again. If the ADIE bit is set to 1, an ADI

interrupt is requested at this time.

5. Steps 2 to 4 are repeated as long as the ADST bit remains set to 1. When the ADST bit is

cleared to 0, A/D conversion stops. After that, if the ADST bit is set to 1, A/D conversion

starts again from the first channel (AN

0).

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