APPENDIX D LIST OF CAUTIONS
User’s Manual U16898EJ3V0UD
394
(8/17)
Chapter
Classification
Function Details
of
Function
Cautions Page
ADCR: 10-bit
A/D conversion
result register
When writing to the A/D converter mode register (ADM) and analog input channel
specification register (ADS), the contents of ADCR may become undefined. Read
the conversion result following conversion completion before writing to ADM and
ADS. Using timing other than the above may cause an incorrect conversion
result to be read.
p. 163
PMC2: Port
mode control
register 2
When PMC20 to PMC23 are set to 1, the P20/ANI0 to P23/ANI3 pins cannot be
used as port pins.
p. 164
Make sure the period of <1> to <4> is 1
µ
s or more.
pp. 165,
169
It is no problem if the order of <1> and <2> is reversed.
pp. 165,
169
<1> can be omitted. However, ignore the data resulting from the first conversion
after <4> in this case.
p. 169
Soft
A/D converter
operations
The period from <5> to <8> differs from the conversion time set using bits 5 to 3
(FR2 to FR0) of ADM. The period from <7> to <8> is the conversion time set
using FR2 to FR0.
p. 169
Operating
current in STOP
mode
The A/D converter stops operating in the STOP mode. At this time, the operating
current can be reduced by clearing bit 7 (ADCS) and bit 0 (ADCE) of the A/D
converter mode register (ADM) to 0.
p. 172
Hard
Input range of
ANI0 to ANI3
Observe the rated range of the ANI0 to ANI3 input voltage. If a voltage of AV
REF
or higher and V
SS
or lower (even in the range of absolute maximum ratings) is
input to an analog input channel, the converted value of that channel becomes
undefined. In addition, the converted values of the other channels may also be
affected.
p. 172
Conflict between A/D conversion result register (ADCR, ADCRH) write and
ADCR, ADCRH read by instruction upon the end of conversion ADCR, ADCRH
read has priority. After the read operation, the new conversion result is written to
ADCR, ADCRH.
p. 172
Soft
Conflicting
operations
Conflict between ADCR, ADCRH write and A/D converter mode register (ADM)
write or analog input channel specification register (ADS) write upon the end of
conversion ADM or ADS write has priority. ADCR, ADCRH write is not
performed, nor is the conversion end interrupt signal (INTAD) generated.
p. 172
Noise
countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to the
AV
REF
pin and ANI0 to ANI3 pins.
<1> Connect a capacitor with a low equivalent resistance and a high frequency
response to the power supply.
<2> Because the effect increases in proportion to the output impedance of the
analog input source, it is recommended that a capacitor be connected
externally, as shown in Figure 9-19, to reduce noise.
<3> Do not switch the A/D conversion function of the ANI0 to ANI3 pins to their
alternate functions during conversion.
<4> The conversion accuracy can be improved by setting HALT mode
immediately after the conversion starts.
p. 173
Chapter 10
Hard
A/D
Converter
ANI0/P20 to
ANI3/P23
The analog input pins (ANI0 to ANI3) are also used as input port pins (P20 to
P23).
When A/D conversion is performed with any of ANI0 to ANI3 selected, do not
access P20 to P23 while conversion is in progress; otherwise the conversion
resolution may be degraded.
p. 173