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CHAPTER 14 10-BIT A/D CONVERTER (
μ
PD780034, 780034Y SUBSERIES)
Figure 14-10. Analog Input Pin Connector
Reference
Voltage
Input
C = 100 to 1000pF
If there is a possibility that noise equal to or higher than AV
REF
or
equal to or lower than AV
SS
may enter, clamp with a diode with a
small V
F
value (0.3 V or lower).
AV
REF
V
DD0
AV
DD
AV
SS
V
SS0
ANI0 to ANI7
(5) ANI0 to ANI7
The analog input pins (ANI0 to ANI7) also function as input/output port pins (P10 to P17).
When A/D conversion is performed with any of pins ANI0 to ANI7 selected, do not execute an input instruction
to port 1 while conversion is in progress, as this may reduce the conversion resolution.
Also, if digital pulses are applied to a pin adjacent to the pin in the process of A/D conversion, the expected
A/D conversion value may not be obtainable due to coupling noise. Therefore, avoid applying pulses to pins
adjacent to the pin undergoing A/D conversion.
(6) AV
REF
pin input impedance
A series resistor string of approx. 10 k
is connected between the AV
REF
pin and the AV
SS
pin.
Therefore, when the output impedance of the reference voltage is too high, it seems as if the AV
REF
pin and the
series resistor string are connected in parallel. This may cause a greater reference voltage error.
(7) Interrupt request flag (ADIF0)
The interrupt request flag (ADIF0) is not cleared even if the analog input channel specification register (ADS0)
is changed.
Therefore, if an analog input pin is changed during A/D conversion, the A/D conversion result and conversion
end interrupt request flag for the pre-change analog input may be set just before the ADS0 rewrite. Caution is
therefore required since, at this time, when ADIF0 is read immediately just after the ADS0 rewrite, ADIF0 is set
despite the fact that the A/D conversion for the post-change analog input has not ended.
When A/D conversion is restarted after it is stopped, clear ADIF0 before restart.