SH7055S Datasheet, PDF (642/1002 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7000 Series

17.4 Operation
The A/D converter operates by successive approximations with 10-bit resolution. It has two
operating modes: single mode and scan mode. There are two kinds of scan mode: continuous and
single-cycle. In single mode, conversion is performed once on one specified channel, then ends. In
continuous scan mode, A/D conversion continues on one or more specified channels until the
ADST bit is cleared to 0. In single-cycle scan mode, A/D conversion ends after being performed
once on one or more channels.
17.4.1 Single Mode
Single mode, should be selected when only one A/D conversion on one channel is required. Single
mode is selected by setting the ADM1 and ADM0 bits in the A/D control/status register (ADSCR)
to 00. When the ADST bit in the A/D control register (ADCR) is set to 1, A/D conversion is
started in single mode.
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 flag in ADCSR is set to 1. If the ADIE bit in ADCSR is also 1,
an ADI interrupt is requested. To clear the ADF flag, first read ADF when set to 1, then write 0 to
ADF. If the DMAC is activated by the ADI interrupt, ADF is cleared automatically.
An example of the operation when analog input channel 1 (AN1) is selected and A/D conversion
is performed in single mode is described next. Figure 17.3 shows a timing diagram for this
example.
1. Single mode is selected (ADM1 = ADM0 = 0), input channel AN1 is selected (CH3 = 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 to ADDR1. 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 is started.
5. The routine reads ADF set to 1, then writes 0 to ADF.
6. The routine reads and processes the conversion result (ADDR1).
7. Execution of the A/D interrupt handling routine ends. After this, if the ADST bit is set to 1,
A/D conversion starts again and steps 2 to 7 are repeated.
Rev.2.0, 07/03, page 604 of 960