H8SLASH3028F datasheet(579/923 Pages) RENESAS

579 / 923 page

Rev. 2.00, 09/03, page 549 of 890

15.4

Operation

The A/D converter operates by successive approximations with 10-bit resolution. It has two

operating modes: single mode and scan mode.

15.4.1

Single Mode (SCAN = 0)

Single mode should be selected when only one A/D conversion on one channel is required. A/D

conversion starts 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.

When conversion ends the ADF bit is set to 1. If the ADIE bit is also set to 1, an ADI interrupt is

requested at this time. To clear the ADF flag to 0, first read ADCSR, then write 0 in ADF.

When the mode or analog input channel must be switched 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 mode or channel is changed.

Typical operations when channel 1 (AN1) is selected in single mode are described next.

Figure 15.3 shows a timing diagram for this example.

1. Single mode is selected (SCAN = 0), input channel AN1 is selected (CH2 = 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 into 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 in 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.

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