![](http://datasheet.mmic.net.cn/Renesas-Electronics-America/UPD78F1168AGF-GAS-AX_datasheet_99857/UPD78F1168AGF-GAS-AX_916.png)
APPENDIX B LIST OF CAUTIONS
User’s Manual U17894EJ9V0UD
914
(15/35)
Chapter
Cl
assi
fi
cati
on
Function
Details of
Function
Cautions
Page
Hard
Noise
countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to the AVREF0
pin and pins ANI0 to ANI15.
<1> Connect a capacitor with a low equivalent resistance and a good frequency
response to the power supply.
<2> The higher the output impedance of the analog input source, the greater the
influence. To reduce the noise, connecting external C as shown in Figure 11-26
is recommended.
<3> Do not switch these pins with other pins during conversion.
<4> The accuracy is improved if the HALT mode is set immediately after the start of
conversion.
p.376
Soft
The analog input pins (ANI0 to ANI7) are also used as input port pins (P20 to P27).
The analog input pins (ANI8 to ANI15) are also used as input port pins (P150 to
P157).
When A/D conversion is performed with any of ANI0 to ANI15 selected, do not
access P20 to P27 and P150 to P157 while conversion is in progress; otherwise the
conversion resolution may be degraded. It is recommended to select pins used as
P20 to P27 and P150 to P157 starting with the ANI0/P20 that is the furthest from
AVREF0.
p.377
ANI0/P20 to
ANI7/P27 and
ANI8/P150 to
ANI15/P157
If a digital pulse is applied to the pins adjacent to the pins currently 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
undergoing A/D conversion.
p.377
Input impedance
of ANI0 to ANI15
pins
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
Ω, and to connect a
capacitor of about 100 pF to the ANI0 to ANI15 pins (see Figure 11-26).
p.377
Hard
AVREF0 pin input
impedance
A series resistor string of several tens of k
Ω is connected between the AVREF0 and
AVSS pins.
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 AVREF0 and AVSS
pins, resulting in a large reference voltage error.
p.377
Interrupt request
flag (ADIF)
The interrupt request flag (ADIF) is not cleared even if the analog input channel
specification register (ADS) is changed.
Therefore, if an analog input pin is changed during A/D conversion, the A/D
conversion result and ADIF for the pre-change analog input may be set just before
the ADS rewrite. Caution is therefore required since, at this time, when ADIF is read
immediately after the ADS rewrite, ADIF is set despite the fact A/D conversion for the
post-change analog input has not ended.
When A/D conversion is stopped and then resumed, clear ADIF before the A/D
conversion operation is resumed.
p.378
Chapter
1
Soft
A/D
converter
Conversion
results just after
A/D conversion
start
The first A/D conversion value immediately after A/D conversion starts may not fall
within the rating range if the ADCS bit is set to 1 within 1
μs after the ADCE bit was
set to 1. Take measures such as polling the A/D conversion end interrupt request
(INTAD) and removing the first conversion result.
p.378