Analog Input Pin Processing - NEC mPD780208 Subseries User Manual

(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
greater than or equal to AV
rating range), the conversion value for that channel will be undefined, and the conversion values of the
other channels may also be affected.
(3) Noise countermeasures
In order to maintain 8-bit resolution, attention must be paid to noise on the AV
Since 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 12-9 in order to reduce noise.
Reference
voltage input
C = 100 to
1000 pF
(4) Pins ANI0/P10 to ANI7/P17
The analog input pins ANI0 to ANI7 also function as I/O port (port 1) pins.
Pins used as analog inputs should be set to the input mode.
When A/D conversion is performed with any of pins ANI0 to ANI7 selected, be sure not to execute an
instruction that inputs data to port 1 while conversion is in progress, as this may reduce the conversion
resolution.
Also, if digital pulses are applied to a pin adjacent to the pin in the process of A/D conversion, the expected
A/D conversion value may not be obtainable due to coupling noise. Therefore, avoid applying pulses
to pins adjacent to the pin undergoing A/D conversion.
(5) AV pin input impedance
REF
A series resistor string of approximately 10 kΩ is connected between the AV
Therefore, if the output impedance of the reference voltage source is high, this will result in series
connection to the series resistor string between the AV
reference voltage error.
CHAPTER 12 A/D CONVERTER
or less than or equal to AV
REF
Figure 12-9. Analog Input Pin Processing
If there is possibility that noise whose
level is AV
clamp with a diode with a small V
AV
REF
User's Manual U11302EJ4V0UM
is input (even if within the absolute maximum
SS
or higher or AV or lower may enter,
REF SS
(0.3 V or less).
F
AV
REF
ANI0 to ANI7
V
DD
AV
DD
AV
SS
V
SS
pin and the AV pin, and there will be a large
REF SS
and ANI0 to ANI7 pins.
REF
pin and the AV pin.
REF SS
203