UPD78F0838 Renesas Electronics Corporation., UPD78F0838 Datasheet - Page 370

• Manufacturer Part Number: UPD78F0838
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

(5) P20/ANI0 to P27/ANI7
(6) Input impedance of ANI0 to ANI7 pins
(7) AV
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<1> The analog input pins (ANI0 to ANI7) are also used as I/O port pins (P20 to P27).
<2> If a digital pulse is applied to the pins adjacent to the pins currently used for A/D conversion, the expected
This A/D converter charges a sampling capacitor for sampling during sampling time.
Therefore, only a leakage current flows when sampling is not in progress, and a current that charges the
capacitor flows during sampling. Consequently, the input impedance fluctuates depending on whether sampling
is in progress, and on the other states.
To make sure that sampling is effective, however, it is recommended to keep the output impedance of the analog
input source to within 10 k , and to connect a capacitor of about 100 pF to the ANI0 to ANI7 pins (see Figure 11-
20. Analog Input Pin Connection).
A series resistor string of several tens of k is connected between the AV
Therefore, if the output impedance of the reference voltage source is high, this will result in a series connection to
the series resistor string between the AV
Reference
C = 100 to 1,000 pF
voltage
REF
input
When A/D conversion is performed with any of ANI0 to ANI7 selected, do not access P20 to P27 while
conversion is in progress; otherwise the conversion resolution may be degraded. It is recommended to
select pins used as P20 to P27 starting with the P20/ANI0 that is the furthest from AV
value of the A/D conversion may not be obtained due to coupling noise. Therefore, do not apply a pulse to
the pins adjacent to the pin undergoing A/D conversion.
pin input impedance
Figure 11-20. Analog Input Pin Connection
Preliminary User’s Manual U19748EJ1V0UD
CHAPTER 11 A/D CONVERTER
REF
and AV
AV
AV
V
ANI0 to ANI7
SS
REF
SS
If there is a possibility that noise equal to or higher than AV
equal to or lower than AV
small V
SS
pins, resulting in a large reference voltage error.
F
value (0.3 V or lower).
SS
REF
may enter, clamp with a diode with a
and AV
SS
pins.
REF
.
REF
or