UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 118

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UPD75238GJ

Manufacturer Part Number
UPD75238GJ
Description
4 BIT SINGLE-CHIP MICROCOMPUTER
Manufacturer
NEC [NEC]
Datasheet
(7) Other notes on use
(a) AN0 to AN7 input range
Specified voltages must be applied to AN0 to AN7 inputs. If a voltage higher than V
V
is applied even when the maximum absolute rating is not exceeded, the conversion result for an
SS
associated channel becomes unpredictable. In addition, the conversion results for other channels
may be affected.
(b) Noise protection
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
connected.
Fig. 4-66 Analog Input Pin Connection
C = 100 – 1000 pF
C
V
(c) AN4/P90 to AN7/P93 pins
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.
(d) AV
pins
DD
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
pin.
DD
118
If it is anticipated that noise voltages do not fall in the
V
range of V
to V
, clamp this point using a diode with
DD
DD
SS
a low V
(not higher than 0.3 V).
F
AV
, AN0 to AN7
REF
PD75238
DD
V
DD
AV
DD
AV
SS
V
SS
PD75238
or lower than
DD
,
REF
pin must be
DD

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