HD64F2357VF13 Datasheet, PDF (578/1049 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

16.4.2 Scan Mode (SCAN = 1)
Scan mode is useful for monitoring analog inputs in a group of one or more channels. When the ADST bit is set to 1 by a
software, timer or external trigger input, A/D conversion starts on the first channel in the group (AN0). When two or
more channels are selected, after conversion of the first channel ends, conversion of the second channel (AN1) starts
immediately. A/D conversion continues cyclically on the selected channels until the ADST bit is cleared to 0. The
conversion results are transferred for storage into the ADDR registers corresponding to the channels.
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 three channels (AN0 to AN2) are selected in scan mode are described next. Figure 16-4 shows a
timing diagram for this example.
[1] Scan mode is selected (SCAN = 1), scan group 0 is selected (CH2 = 0), analog input channels AN0 to AN2 are
selected (CH1 = 1, CH0 = 0), and A/D conversion is started (ADST = 1)
[2] When A/D conversion of the first channel (AN0) is completed, the result is transferred to ADDRA. Next, conversion
of the second channel (AN1) starts automatically.
[3] Conversion proceeds in the same way through the third channel (AN2).
[4] When conversion of all the selected channels (AN0 to AN2) is completed, the ADF flag is set to 1 and conversion of
the first channel (AN0) starts again. If the ADIE bit is set to 1 at this time, an ADI interrupt is requested after A/D
conversion ends.
[5] Steps [2] to [4] are repeated as long as the ADST bit remains set to 1. When the ADST bit is cleared to 0, A/D
conversion stops. After that, if the ADST bit is set to 1, A/D conversion starts again from the first channel (AN0).
ADST
ADF
State of channel 0 (AN0) _Idle
Set*¹
Continuous A/D conversion execution
Clear*¹
Clear*¹
A/D conversion 1
Idle
A/D conversion time
A/D conversion 4
Idle
State of channel 1 (AN1)
Idle
A/D conversion 2
Idle
A/D conversion 5 *² Idle
State of channel 2 (AN2)
Idle
A/D conversion 3
Idle
State of channel 3 (AN3)
ADDRA
Idle
Transfer
A/D conversion result 1
A/D conversion result 4
ADDRB
A/D conversion result 2
ADDRC
A/D conversion result 3
ADDRD
Notes: 1. Vertical arrows ( ) indicate instructions executed by software.
2. Data currently being converted is ignored.
Figure 16-4 Example of A/D Converter Operation
(Scan Mode, Channels AN0 to AN2 Selected)
Rev.6.00 Oct.28.2004 page 548 of 1016
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