upd78f0114hgb-8es-a Renesas Electronics Corporation., upd78f0114hgb-8es-a Datasheet - Page 489

• Manufacturer Part Number: upd78f0114hgb-8es-a
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

A/D
Converter
Function
Conflicting
operations
Noise
countermeasures
ANI0/P20 to
ANI7/P27
Input
impedance of
ANI0 to ANI7
pins
AV
impedance
Interrupt
request flag
(ADIF)
REF
Details of
Function
pin input
In case of conflict between A/D conversion result register (ADCR) write and ADCR
read by instruction upon the end of conversion,
ADCR read has priority. After the read operation, the new conversion result is
written to ADCR.
In case of conflict between ADCR 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 write is not performed, nor is
the conversion end interrupt signal (INTAD) generated.
To maintain the 10-bit resolution, attention must be paid to noise input to the
AV
the output impedance of the analog input source, it is recommended that a
capacitor be connected externally, as shown in Figure 11-19, to reduce noise.
The analog input pins (ANI0 to ANI7) are also used as input port pins (P20 to
P27).
When A/D conversion is performed with any of ANI0 to ANI7 selected, do not
access port 2 while conversion is in progress; otherwise the conversion resolution
may be degraded.
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.
In this A/D converter, the internal sampling capacitor is charged and sampling is
performed for approx. one sixth of the conversion time.
Since only the leakage current flows other than during sampling and the current
for charging the capacitor also flows during sampling, the input impedance
fluctuates and has no meaning.
To perform sufficient sampling, however, it is recommended to make the output
impedance of the analog input source 10 k
around 100 pF to the ANI0 to ANI7 pins (see Figure 11-19).
A series resistor string of several tens of k
AV
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 AV
AV
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.
REF
SS
SS
pins.
pins, resulting in a large reference voltage error.
pin and pins ANI0 to ANI7. Because the effect increases in proportion to
APPENDIX D LIST OF CAUTIONS
User’s Manual U16961EJ4V0UD
Cautions
is connected between the AV
or lower, or attach a capacitor of
REF
REF
and
and
p. 238
p. 238
p. 239
p. 239
p. 239
p. 239
p. 239
p. 240
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