SH7721 datasheet(1000/1524 Pages) RENESAS

1000 / 1524 page

Section 27

A/D Converter

Rev. 3.00

Jan. 18, 2008

Page 938 of 1458

REJ09B0033-0300

27.4.2

Multi Mode

Multi mode should be selected when performing A/D conversions on one or more channels. When

the ADST bit in the A/D conversion control/status register (ADCSR) is set to 1 by software, A/D

conversion starts on the first channel (AN0). When two or more channels are selected, after

conversion of the first channel ends, conversion of the second channel (AN1) starts immediately.

When A/D conversions end on the selected channels, 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 A/D conversion, to

prevent incorrect operation, first clear the ADST bit to 0 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 (AN0 to AN2) are selected in scan mode are described

next. Figure 27.3 shows a timing diagram for this example.

1. Start the clock supply to the ADC module (clear the MSTP33 bit in STBCR3 to 0) to run the

ADC module.

2. Multi mode is selected (MULTI = 1), analog input channels AN0 to AN2 are selected (CH1 =

1, CH0 = 0), and A/D conversion is started (ADST = 1).

3. When A/D conversion of the first channel (AN0) is completed, the result is transferred into

ADDRA.

4. Next, conversion of the second channel (AN1) starts automatically.

5. Conversion proceeds in the same way through the third channel (AN2).

6. When conversion of all selected channels (AN0 to AN2) is completed, the ADF flag is set to 1

and ADST bit is cleared to 0. If the ADIE bit is set to 1, an ADI interrupt is requested at this

time.

7. Stop the clock supply to the ADC module (set the MSTP33 bit in STBCR3 to 1) to place the

ADC in the module standby state.

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