UPD78F0988AGC-8BS Renesas Electronics America, UPD78F0988AGC-8BS Datasheet - Page 216

• Manufacturer Part Number: UPD78F0988AGC-8BS
• Manufacturer: Renesas Electronics America

Specifications of UPD78F0988AGC-8BS

• Lead Free Status / Rohs Status: Supplier Unconfirmed

214
(4) Countermeasures against noise
(5) ANI0/P10 to ANI7/P17
(6) Input impedance of ANI0 to ANI7 pins
(7) Input impedance to AV
To keep the resolution of 10 bits, noise superimposed on the AV
as much as possible. The higher the output impedance of the analog input source, the greater the effect. To
suppress noise, connecting an external capacitor as shown in Figure 11-9 is recommended.
The analog input pins (ANI0 to ANI7) are also used as input port pins (P10 to P17).
When A/D conversion is performed with any of ANI0 to ANI7 selected, do not execute the input instruction
to port 1 while conversion is in progress; otherwise, the conversion resolution may be degraded.
If a digital pulse is applied to the pins adjacent to the pin currently being used for A/D conversion, the expected
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 under going A/D conversion.
This A/D converter charges the internal sampling capacitor for about 1/10 of the conversion time, and performs
sampling.
Therefore at times other than sampling, only the leak current is output. During sampling, the current for
charging the capacitor is also output, so the input impedance fluctuates and has no meaning.
However, to ensure adequate sampling, it is recommended that the output impedance of the analog input
source be set to below 10 k , or a 100 pF capacitor be connected to the ANI0 to ANI7 pins (see Figure 11-
9).
A series resistor string of several 10 k
If the output impedance of the reference voltage source is high, therefore, the reference voltage error increases
when connecting the impedance in series with the series resistor string between the AV
voltage input
Reference
C = 100 to
1000 pF
REF
Figure 11-9. Processing Analog Input Pin
pin
AV
REF
CHAPTER 11 A/D CONVERTER
User’s Manual U13029EJ7V1UD
is connected between the AV
If there is a possibility that noise of
AV
clamp the noise by using a diode with a low V
REF
or higher, or AV
AV
ANI0 to ANI7
V
AV
AV
V
DD0
SS0
REF
DD
SS
SS
REF
or lower is input,
and ANI0 to ANI7 pins must be suppressed
REF
and AV
SS
F
(0.3 V MAX.).
pins.
REF
and AV
SS
pins.