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CHAPTER 13
A/D CONVERTER
User’s Manual U12697EJ4V1UD
13.4 Operations
13.4.1 Basic operations of A/D converter
<1>
Select one channel for A/D conversion with the A/D converter input selection register (ADIS).
<2>
The voltage input to the selected analog input channel is sampled by the sample & hold circuit.
<3>
After sampling has been performed for a certain time, the sample & hold circuit enters the hold status, and the
input analog voltage is held until A/D conversion ends.
<4>
Bit 7 of the successive approximation register (SAR) is set. The tap selector sets the voltage tap for the series
resistance string at (1/2)AVDD.
<5>
The difference in voltage between the series resistance string's voltage tap and analog input is compared with
the voltage comparator. If the analog input is greater than (1/2)AVDD, the setting for the MSB in SAR will remain
the same. If it is smaller than (1/2)AVDD, the MSB will be reset.
<6>
Next, bit 6 of SAR is automatically set, and the next comparison is started. The series resistor string voltage
tap is selected as shown below according to bit 7 to which a result has already been set.
 Bit 7 = 1: (3/4)AVDD
 Bit 7 = 0: (1/4)AVDD
The voltage tap and analog input voltage are compared, and bit 6 of SAR is manipulated according to the result,
as follows.
 Analog input voltage
≥ Voltage tap: Bit 6 = 1
 Analog input voltage < Voltage tap: Bit 6 = 0
<7>
Comparisons of this kind are repeated until bit 0 of SAR.
<8>
When comparison of all eight bits is completed, the valid digital result remains in SAR, and this value is
transferred to the A/D conversion result and latched.
At the same time, it is possible to issue an A/D conversion end interrupt request (INTAD).
Caution
The value of the first A/D conversion is undefined if ADCS is set when bit 0 (ADCE) of the A/D
converter mode register (ADM) is 0.