SH7018 datasheet(284/431 Pages) RENESAS

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13.4

Operation

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

operating modes: single mode and scan mode.. The operation in these two modes is described

below.

13.4.1

Single Mode (SCAN = 0)

Single mode should be selected for A/D conversion on only one channel. A/D conversion starts

when the ADST bit in the A/D control/status register (ADCSR) is set to 1 by software or MTU

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 in ADCSR is set to 1. If the ADIE bit in ADCSR is also 1, an

ADI interrupt is requested. To clear the ADF bit, first read ADF when set to 1, then write 0 in

ADF.

To prevent incorrect operation, A/D conversion should be halted by clearing the ADST bit to 0

before changing the mode or analog input channel. After the change is made, A/D conversion is

restarted by setting the ADST bit to 1 (the mode or channel change and setting of the ADST bit

can be carried out simultaneously).

An example of the operation when analog input channel 1 (AN1) is selected and A/D conversion

is performed in single mode is described below. Figure 13.3 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 request 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

ADF is set to 1, ADST 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 service routine is started.

5. The routine reads ADF set to 1, then writes 0 in ADF.

6. The routine reads and processes the conversion result (ADDRB).

7. Execution of the A/D interrupt service routine ends. After this, if the ADST bit is set to 1, A/D

conversion starts again and steps 2 to 7 are repeated.

SH7018 Datasheet(PDF) 284 Page - Renesas Technology Corp