APPENDIX D LIST OF CAUTIONS
User’s Manual U18172EJ2V0UD
315
(8/15)
Chapter
Cl
assi
fi
cati
on
Function Details
of
Function
Cautions Page
ADS: Analog
input channel
specification
register
Be sure to clear bits 2 to 7 of ADS to 0.
p. 155
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. 155
PMC2: Port
mode control
register 2
If PMC20 to PMC23 are set to 1, the P20/ANI0/TI000/TOH1,
P21/ANI1/TIO10/TO00/INTP0, P22/ANI2, and P23/ANI3 pins cannot be used for
any purpose other than the A/D converter function.
Be sure to set 0 to the Pull-up resistor option register of the pin set in A/D
converter mode.
p. 156
Make sure the period of <1> to <4> is 1
µ
s or more.
pp. 157,
161
It is no problem if the order of <1> and <2> is reversed.
pp. 157,
161
<1> can be omitted. However, ignore the data resulting from the first conversion
after <4> in this case.
p. 161
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. 161
Operating
current in STOP
mode
To satisfy the DC characteristics of supply current in STOP mode, clear bit 7
(ADCS) and bit 0 (ADCE) of the A/D converter mode register (ADM) to 0 before
executing the STOP instruction.
p. 164
Hard
Input range of
ANI0 to ANI3
Observe the rated range of the ANI0 to ANI3 input voltage. If a voltage of V
DD
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. 164
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. 164
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. 164
Chapter 9
Hard
A/D
Converter
Noise
countermeasures
To maintain the 10-bit resolution, attention must be paid to noise input to the V
DD
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. 164