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CHAPTER 14 10-BIT A/D CONVERTER (
μ
PD780034, 780034Y SUBSERIES)
14.5 A/D Converter Cautions
(1) Current consumption in standby mode
A/D converter stops operating in the standby mode. At this time, current consumption can be reduced by stopping
the conversion operation (by setting bit 7 (ADCS0) of the A/D converter mode register (ADM0) to 0).
Figure 14-9 shows how to reduce the current consumption in the standby mode.
Figure 14-9. Example of Method of Reducing Current Consumption in Standby Mode
AV
REF
AV
SS
P-ch
Series resistor string
ADCS0
(2) Input range of ANI0 to ANI7
The input voltages of ANI0 to ANI7 should be within the specification range. In particular, if a voltage higher
than AV
REF
or lower than AV
SS
is input (even if within the absolute maximum rating range), the conversion value
of that channel will be undefined and the conversion values of other channels may also be affected.
(3) Contending operations
<1>
Contention between A/D conversion result register (ADCR0) write and ADCR0 read by instruction
upon the end of conversion
ADCR0 read is given priority. After the read operation, the new conversion result is written to ADCR0.
<2>
Contention between ADCR0 write and external trigger signal input upon the end of conversion
The external trigger signal is not accepted during A/D conversion. Therefore, the external trigger signal
is not accepted during ADCR0 write.
<3>
Contention between ADCR0 write and A/D converter mode register (ADM0) write or analog input
channel specification register (ADS0) write
ADM0 or ADS0 write is given priority. ADCR0 write is not performed, nor is the conversion end interrupt
request signal (INTAD0) generated.
<4>
Noise countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to pin AV
REF
and pins ANI0 to ANI7.
Because the effect increases in proportion to the output impedance of the analog input source, it is
recommended that a capacitor be connected externally as shown in Figure 14-10 to reduce noise.