UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 118
Manufacturer Part Number
4 BIT SINGLE-CHIP MICROCOMPUTER
(7) Other notes on use
(a) AN0 to AN7 input range
(b) Noise protection
(c) AN4/P90 to AN7/P93 pins
Specified voltages must be applied to AN0 to AN7 inputs. If a voltage higher than V
associated channel becomes unpredictable. In addition, the conversion results for other channels
may be affected.
To maintain 8-bit resolution, the user should pay attention to noise that may be applied to the AV
and AN0 to AN7 pins. Noise adversely affects operation to a greater extent when the analog input
source has a higher output impedance. As shown in Fig. 4-66, a capacitor should be externally
The analog input pins (AN4 to AN7) are also used for an input port (port 9).
When any of AN4 to AN7 is selected for A/D conversion, no input instruction must be executed for
port 9 during A/D conversion. Otherwise, the accuracy of conversion may deteriorate.
If a digital pulse signal is applied to a pin adjacent to a pin being used for A/D conversion, an expected
A/D conversion value may not be obtained because of coupling noise.
So no digital pulse signal should be applied to the adjacent pin being used for A/D conversion.
When the A/D converter is not used or is in the standby mode, the potential of the AV
equal to that of the V
is applied even when the maximum absolute rating is not exceeded, the conversion result for an
C = 100 – 1000 pF
Fig. 4-66 Analog Input Pin Connection
If it is anticipated that noise voltages do not fall in the
range of V
a low V
, AN0 to AN7
(not higher than 0.3 V).
, clamp this point using a diode with
or lower than
pin must be