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APPENDIX B LIST OF CAUTIONS
User’s Manual U17854EJ9V0UD
839
(15/33)
Chapter
Cl
assi
fi
cati
on
Function
Details of
Function
Cautions
Page
Input impedance
of ANI0 to ANI7
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 ANI7 pins (see Figure 10-26).
p.330
Hard
AVREF pin input
impedance
A series resistor string of several tens of k
Ω is connected between the AVREF 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 AVREF and AVSS
pins, resulting in a large reference voltage error.
p.330
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.331
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.331
A/D conversion
result register
(ADCR,
ADCRH) read
operation
When a write operation is performed to the A/D converter mode register (ADM),
analog input channel specification register (ADS), and A/D port configuration register
(ADPC), the contents of ADCR and ADCRH may become undefined.
Read the
conversion result following conversion completion before writing to ADM, ADS, and
ADPC.
Using a timing other than the above may cause an incorrect conversion
result to be read.
p.331
Chapter
1
0
Soft
A/D
converter
Starting the A/D
converter
Start the A/D converter after the AVREF voltage stabilize.
p.332
Configuration
of serial
array unit
SDRmn: Lower
8 bits of the
serial data
register mn
Be sure to clear bit 8 to “0”.
p.340
When setting serial array unit m, be sure to set SAUmEN to 1 first. If SAUmEN = 0,
writing to a control register of serial array unit m is ignored, and, even if the register is
read, only the default value is read (except for input switch control register (ISC),
noise filter enable register (NFEN0), port input mode register (PIM0), port output
mode register (POM0), port mode registers (PM0, PM1), and port registers (P0, P1)).
p.342
After setting the PER0 register to 1, be sure to set the SPSm register after 4 or more
clocks have elapsed.
p.342
PER0:
Peripheral
enable register 0
Be sure to clear bits 1 and 6 of PER0 register to 0.
p.342
Be sure to clear bits 15 to 8 to “0”.
p.343
Chapter
1
Soft
Registers
controlling
serial array
unit
SPSm: Serial
clock select
register m
After setting the PER0 register to 1, be sure to set the SPSm register after 4 or more
clocks have elapsed.
p.343