
CHAPTER 10 8-BIT A/D CONVERTER (
PD789407A SUBSERIES)
User’s Manual U13952EJ3V1UD
149
10.5 Cautions on Using 8-Bit A/D Converter
(1)
Current consumption in the standby mode
When the A/D converter enters the standby mode, it stops operating. Stopping conversion (bit 7 (ADCS0) of
A/D converter mode register 0 (ADM0) = 0) can reduce the current consumption.
Figure 10-7 shows how to reduce the current consumption in the standby mode.
Figure 10-7. How to Reduce Current Consumption in Standby Mode
AVREF
AVSS
P-ch
Series resistor string
ADCS0
(2)
Input range for the ANI0 to ANI6 pins
Be sure to keep the input voltage at ANI0 to ANI6 within the rated range. If a voltage greater than AVREF or
less than AVSS (even within the absolute maximum rating) is input to a conversion channel, the conversion
output of the channel becomes undefined, and the conversion output of the other channels may also be
affected.
(3)
Conflict
<1> Conflict between writing to A/D conversion result register 0 (ADCR0) at the end of conversion and reading
from the ADCR0 bit
Reading from the ADCR0 bit takes precedence. After reading, the new conversion result is written to the
ADCR0 bit.
<2> Conflict between writing to the ADCR0 bit at the end of conversion and writing to A/D converter mode
register 0 (ADM0) or A/D input selection register 0 (ADS0)
Writing to ADM0 or ADS0 takes precedence. A request to write to the ADCR0 bit is ignored. No A/D
conversion end interrupt request signal (INTAD0) is generated.
(4)
Conversion results immediately following start of A/D conversion
The first A/D conversion value immediately following the start of A/D conversion may be undefined. Be sure
to poll the A/D conversion end interrupt request (INTAD0) and perform processing such as discarding the first
conversion result.
(5)
Timing that makes the A/D conversion result undefined
If the timing of the end of A/D conversion and the timing of the stop of operation of the A/D converter conflict,
the A/D conversion value may be undefined. Because of this, be sure to read out the A/D conversion result
while the A/D converter is in operation. Furthermore, when reading out an A/D conversion result after A/D
conversion has stopped, be sure to have done so by the time the next conversion result is complete.
The conversion result readout timing is shown in Figures 10-8 and 10-9.