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CHAPTER 10 A/D CONVERTER
User’s Manual U15104EJ2V0UD
(1) Successive approximation register (SAR)
This register compares the analog input voltage value to the voltage tap (compare voltage) value applied from
the series resistor string and holds the result from the most significant bit (MSB).
When up to the least significant bit (LSB) is set (termination of A/D conversion), the SAR contents are
transferred to the A/D conversion result register.
(2) A/D conversion result register 3 (ADCR3)
This register is an 8-bit register to store the A/D conversion result. Each time A/D conversion terminates, the
conversion result is loaded from the successive approximation register (SAR).
ADCR is read with an 8-bit memory manipulation instruction.
Reset input makes ADCR undefined.
Caution
When data is written to A/D converter mode register 3 (ADM3) and analog input channel
specification register 3 (ADS3), the contents of ADCR3 may be undefined. Read the result
of conversion after conversion has been completed and before writing data to ADM3 and
ADS3; otherwise the correct conversion result may not be read.
(3) Power-fail comparison threshold value register 3 (PFT3)
This register sets a threshold value to be compared with the value of A/D conversion result register 3 (ADCR3).
PFT3 is read or written with an 8-bit memory manipulation instruction.
(4) Sample & hold circuit
The sample & hold circuit samples each analog input signal sequentially applied from the input circuit and
sends it to the voltage comparator. This circuit holds the sampled analog input voltage value during A/D
conversion.
(5) Voltage comparator
The voltage comparator compares the analog input to the series resistor string output voltage.
(6) Resistor string
The resistor string is connected between V
DD
and GND, and generates a voltage to be compared to the analog
input.
(7) ANI0 to ANI5 pins
These are the 6-channel analog input pins through which analog signals to undergo A/D conversion are input
to the A/D converter.
Cautions 1. Use the ANI0 to ANI5 input voltages within the specified range. If a voltage higher than
V
DD
or lower than GND is applied (even if within the absolute maximum ratings), the
converted value of the corresponding channel becomes undefined and may adversely
affect the converted values of other channels.
2. The analog input pins (ANI0 to ANI5) are also used as input port pins (P10 to P15). When
one of ANI0 to ANI5 is selected for A/D conversion, do not execute an input instruction
to port 1; otherwise the conversion resolution may drop.
If a digital pulse is applied to the pin adjacent to the pin executing A/D conversion, the
A/D conversion value may not be obtained as expected due to coupling noise. Do not
apply a pulse to the pin adjacent to the pin executing A/D conversion.
Содержание mPD178053
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