CHAPTER 11 A/D CONVERTER
User’s Manual U13850EJ4V0UM
356
11.5 Low Power Consumption Mode
The V850/SB1 and V850/SB2 feature a function that can cut or connect the current between AV
DD
and AV
REF
.
Switching can be performed by setting A/D converter mode register 2 (ADM2).
When AV
DD
=
AV
REF
, and when the system does not require high precision, current consumption can be reduced
by connecting AV
DD
and AV
REF
in the normal mode or disconnecting them in standby mode after opening the AV
REF
pin.
The conversion precision of the reference voltage is reduced since the reference voltage is supplied from AV
DD
via
a switch.
When the A/D converter is not used, cut the tap selector that reduces the current when A/D conversion is stopped
(ADCS = 0), and the supply voltage (AV
DD
), in order to reduce the current consumption.
•
Set the ADPS bit of A/D converter mode register 1 (ADM1) to “1”.
•
Clear the IEAD bit of A/D converter mode register 2 (ADM2) to “0”.
When the ADPS bit is cleared to “0” (comparator on) again, a stabilization time (5
µ
s max.) is required until the
A/D converter is started. Therefore, use software to ensure that a wait time of 5
µ
s elapses.
11.6 Cautions
(1) Current consumption in standby mode
The A/D converter stops operation in the STOP and IDLE modes (operable in the HALT mode). At this time, the
current consumption of the A/D converter can be reduced by stopping the conversion (by resetting the bit 7
(ADCS) of A/D converter mode register 1 (ADM1) to 0).
To reduce the current consumption in the STOP and IDLE modes, set the AV
REF
potential in the user circuit to
the same value (0 V) as the AV
SS
potential.
(2) Input range of ANI0 to ANI11
Keep the input voltage of the ANI0 to ANI11 pins to within the rated range. If a voltage greater than AV
REF
or
lower than AV
SS
(even within the range of the absolute maximum ratings) is input to a channel, the converted
value of the channel becomes undefined. Moreover, the values of the other channels may also be affected.
(3) Conflict
<1> Conflict between writing A/D conversion result register (ADCR) and reading ADCR at end of
conversion
Reading ADCR takes precedence. After ADCR has been read, a new conversion result is written to ADCR.
<2> Conflict between writing ADCR and external trigger signal input at end of conversion
The external trigger signal is not input during A/D conversion. Therefore, the external trigger signal is not
accepted during writing of ADCR.
<3> Conflict between writing of ADCR and writing A/D converter mode register 1 (ADM1) or analog input
channel specification register (ADS)
When ADM1 or ADS write is performed immediately after ADCR write following A/D conversion end, the
conversion result is written to the ADCR register, but the timing is such that INTAD is not generated.
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