H8S2245 datasheet(555/818 Pages) RENESAS

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Section 14 A/D Converter

Rev.3.00 Mar. 26, 2007 Page 513 of 772

REJ09B0355-0300

14.4

Operation

The A/D converter operates by successive approximation 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, according to the software or 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 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 (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 connection 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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