
CHAPTER 13 A/D CONVERTER
Preliminary User’s Manual U16541EJ1V0UM
352
13.4 Operation
13.4.1 Basic operation
<1> Set the operation mode, trigger mode, and conversion time for executing A/D conversion by using the
ADA0M0, ADA0M1, ADA0M2, and ADA0S registers. When the ADA0CE bit of the ADA0M0 register is set,
conversion is started in the software trigger mode and the A/D converter waits for a trigger in the external
timer trigger mode.
<2> When A/D conversion is started, the voltage input to the selected analog input channel is sampled by the
sample & hold circuit.
<3> When the sample & hold circuit samples the input channel for a specific time, it enters the hold status, and
holds the input analog voltage until the A/D conversion is completed.
<4> Set bit 9 of the successive approximation register (SAR). The tap selector selects (1/2) AVREF0 as the voltage
tap of the series resistor string.
<5> The voltage difference between the voltage of the series resistor string and the analog input voltage is
compared by the voltage comparator. If the analog input voltage is higher than (1/2) AVREF0, the MSB of the
SAR register remains set. If it is lower than (1/2) AVREF0, the MSB is reset.
<6> Next, bit 8 of the SAR register is automatically set and the next comparison is started. Depending on the
value of bit 9 to which a result has been already set, the voltage tap of the series resistor string is selected as
follows.
Bit 9 = 1: (3/4) AVREF0
Bit 9 = 0: (1/4) AVREF0
This voltage tap and the analog input voltage are compared and, depending on the result, bit 8 is
manipulated as follows.
Analog input voltage
≥ Voltage tap: Bit 8 = 1
Analog input voltage
≤ Voltage tap: Bit 8 = 0
<7> This comparison is continued to bit 0 of the SAR register.
<8> When comparison of the 10 bits has been completed, the valid digital result is stored in the SAR register,
which is then transferred to and stored in the ADA0CRn register. At the same time, an A/D conversion end
interrupt request signal (INTAD) is generated.