Operation; Single Mode; Scan Mode - Hitachi H8S/2378, H8S/2378R Series Hardware Manual

17.4

Operation

The A/D converter operates by successive approximation with 10-bit resolution. It has two
operating modes: single mode and scan mode. When changing the operating mode or analog input
channel, to prevent incorrect operation, first clear the bit ADST to 0 in ADCSR to halt A/D
conversion. The ADST bit can be set at the same time as the operating mode or analog input
channel is changed.
17.4.1

Single Mode

In single mode, A/D conversion is to be performed only once on the specified single channel.
Operations are as follows.
1. A/D conversion is started when the ADST bit in ADCSR is set to 1, according to the software
or external trigger input.
2. When A/D conversion is completed, the result is transferred to the corresponding A/D data
register to the channel.
3. On completion of conversion, the ADF bit in ADCSR is set to 1. If the ADIE bit is set to 1 at
this time, an ADI interrupt request is generated.
4. The ADST bit remains set to 1 during A/D conversion, and is automatically cleared to 0 when
conversion ends. When the ADST bit is cleared to 0 during A/D conversion, A/D conversion
stops and the A/D converter enters wait state.
17.4.2

Scan Mode

In scan mode, A/D conversion is to be performed sequentially on the specified channels:
maximum four channels or maximum eight channels. Operations are as follows.
1. When the ADST bit in ADCSR is set to 1 by a software, TPU or external trigger input, A/D
conversion starts on the first channel in the group.
The consecutive A/D conversion on maximum four channels (SCANE and SCANS = 10) or on
maximum eight channels (SCANE and SCANS = 11) can be selected. When the consecutive
A/D conversion is performed on the four channels, the A/D conversion starts on AN0 when
CH3 and CH2 =00, AN4 when CH3 and CH2 = 01, AN8 when CH3 and CH2 = 10, or AN12
when CH3 and CH2 = 11. When the consecutive A/D conversion is performed on the eight
channels, the A/D conversion starts on AN0 when SH3 =0 and on AN8 when SH3 =1.
2. When A/D conversion for each channel is completed, the result is sequentially transferred to
the corresponding A/D data register to each channel.
3. When conversion of all the selected channels is completed, the ADF bit in ADCSR is set to 1.
If the ADIE bit is set to 1 at this time, an ADI interrupt is requested. Conversion of the first
channel in the group starts again.
Rev. 1.0, 09/01, page 744 of 904