H8S2245 datasheet(557/818 Pages) RENESAS

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Section 14 A/D Converter

Rev.3.00 Mar. 26, 2007 Page 515 of 772

REJ09B0355-0300

14.4.2

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 a software, timer or external trigger input, A/D conversion starts on the

first channel in the group (AN0). When two or more channels are selected, after conversion of the

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

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 three channels (AN0 to AN2) are selected in scan mode are described

next. Figure 14.4 shows a timing diagram for this example.

[1] Scan mode is selected (SCAN = 1), analog input channels AN0 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 (AN0) is completed, the result is transferred to

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

[3] Conversion proceeds in the same way through the third channel (AN2).

[4] When conversion of all the selected channels (AN0 to AN2) is completed, the ADF flag is set

to 1 and conversion of the first channel (AN0) starts again. If the ADIE bit is set to 1 at this

time, an ADI interrupt is requested after A/D conversion ends.

[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 (AN0).

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