UPD78F9500MA-CAC-A Datasheet, PDF (176/342 Pages) Renesas Technology Corp – 8-Bit Single-Chip Microcontrollers

CHAPTER 9 A/D CONVERTER (μPD78F920x ONLY)
(5) ANI0/P20 to ANI3/P23
<1> The analog input pins (ANI0 to ANI3) are also used as I/O 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.
<2> 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.
(6) Input impedance of ANI0 to ANI3 pins
In this A/D converter, the internal sampling capacitor is charged and sampling is performed during sampling 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 both during sampling and otherwise.
If the shortest conversion time of the reference voltage is used, to perform sufficient sampling, it is recommended
to make the output impedance of the analog input source 1 kΩ or lower, or attach a capacitor of around 0.01 μF
to 0.1 μF to the ANI0 to ANI3 pins (see Figure 9-19).
When writing the flash memory on-board, supply a stabilized analog voltage to the ANI2 and ANI3 pins, without
attaching a capacitor. Because the communication pulse may change and the communication may fail if a
capacitor is attached to remove noise.
(7) 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.
Figure 9-20. Timing of A/D Conversion End Interrupt Request Generation
ADS rewrite
(start of ANIn conversion)
ADS rewrite
(start of ANIm conversion)
ADIF is set but ANIm conversion
has not ended.
A/D conversion
ANIn
ANIn
ANIm
ANIm
ADCR,
ADCRH
ADIF
Remarks 1. n = 0 to 3
2. m = 0 to 3
174
ANIn
ANIn
ANIm
ANIm
User’s Manual U18172EJ3V0UD