NEC uPD78P078 - Manual (Page 307)

307
CHAPTER 15 A/D CONVERTER
(5) AV
REF0
pin input impedance
A series resistor string of approximately 10 k
Ω
is connected between the AV
REF0
pin and the AV
SS
pin.
Therefore, if the output impedance of the reference voltage source is high, this will result in parallel
connection to the series resistor string between the AV REF0 pin and the AV SS pin, and there will be a large
reference voltage error.
(6) Interrupt request flag (ADIF)
The interrupt request flag (ADIF) is not cleared even if the A/D converter mode register (ADM) is changed.
Caution is therefore required since, if an analog input pin is changed during A/D conversion, the A/D
conversion result and ADIF for the pre-change analog input may be set just before the ADM rewrite, and
when ADIF is read immediately after the ADM rewrite, ADIF may be set despite the fact that the A/D
conversion for the post-change analog input has not ended.
When the A/D conversion is stopped and then resumed, clear the ADIF before it is resumed.
Figure 15-11. A/D Conversion End Interrupt Request Generation Timing
Remark n = 0, 1, ... , 7
m = 0, 1, ... , 7
(7) AV DD pin
The AV DD pin is the analog circuit power supply pin, and supplies power to the input circuits of ANI0/P10
to ANI7/P17.
Therefore, be sure to apply the same voltage as V DD to this pin even when the application circuit is designed
so as to switch to a backup battery.
Figure 15-12. Handling of AV DD Pin
Main
power
supply
AV REF0
V DD
AV DD
AV
SS
V
SS
Capacitor
for back-up
A /D Conversion
ADCR
INTAD
ANIn ANIn ANIm ANIm
ANIn ANIn ANIm ANIm
ADM Rewrite
(Start of ANIn Conversion)
ADM Rewrite
(Start of ANIm Conversion)
INTAD is set but ANIm
conversion has not ended