Cautions For A/D Converter - NEC mPD780024AS Series Preliminary User's Manual

CHAPTER 11 8-BIT A/D CONVERTER ( µ PD780024AS SUBSERIES)

11.6 Cautions for A/D Converter

(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 0 (ADM0) to 0).
Figure 11-15 shows how to reduce the current consumption in the standby mode.
Figure 11-15. Example of Method of Reducing Current Consumption in Standby Mode
(2) Input range of ANI0 to ANI3
The input voltages of ANI0 to ANI3 should be within the specification range. In particular, if a voltage higher
than AV or lower than AV
REF
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 0 (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 0 (ADM0) write or analog input channel
specification register 0 (ADS0) write upon the end of conversion
ADM0 or ADS0 write is given priority. ADCR0 write is not performed, nor is the conversion end interrupt
request signal (INTAD0) generated.
186
AV
REF
P-ch
Series resistor string
AV
SS
is input (even if within the absolute maximum rating range), the conversion value
SS
Preliminary User's Manual U16035EJ1V0UM
ADCS0