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Chapter 20
A/D Converter (ADC)
Preliminary User’s Manual U17566EE1V2UM00
(3)
Power-fail compare threshold value register (ADA0PFT)
The ADA0PFT register sets a threshold value that is compared with the value
of A/D conversion result register nH (ADCR0Hn). The 8-bit data set to the
ADA0PFT register is compared with the higher 8 bits of the A/D conversion
result register (ADCR0Hn).
This register can be read or written in 8-bit or 1-bit units.
Reset input clears this register to 00H.
(4)
Sample & hold circuit
The sample & hold circuit samples each of the analog input signals selected by
the input circuit and sends the sampled data to the voltage comparator. This
circuit also holds the sampled analog input signal voltage during A/D
conversion.
(5)
Voltage comparator
The voltage comparator compares a voltage value that has been sampled and
held with the voltage value of the series resistor string.
(6)
Series resistor string
This series resistor string is connected between AV
REF
and AV
SS
and generates
a voltage for comparison with the analog input signal.
(7)
ANIn pins
These are analog input pins for the 16 A/D Converter channels and are used to
input analog signals to be converted into digital signals. Pins other than the
one selected as the analog input by the ADA0S register can be used as input
port pins.
Caution
1.
Make sure that the voltages input to the ANIn pins do not exceed the rated
values. In particular if a voltage of AV
REF
or higher is input to a channel, the
conversion value of that channel becomes undefined, and the conversion
values of the other channels may also be affected.
2.
The analog input pins ANIn function also as input port pins. If any of ANIn is
selected and A/D converted, do not execute an input instruction this ports
during conversion. If executed, the conversion resolution may be degraded.
(8)
AV
REF
pin
This is the pin used to input the reference voltage of the A/D Converter. The
signals input to the ANIn pins are converted to digital signals based on the
voltage applied between the AV
REF
and AV
SS
pins.
(9)
AV
SS
pin
This is the ground pin of the A/D Converter. Always make the potential at this
pin the same as that at the V
SS
pin even when the A/D Converter is not used.
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