
CHAPTER 13 A/D CONVERTER
User
’
s Manual U15862EJ3V0UD
428
13.5 Operation
13.5.1 Basic operation
<1> Select one channel whose analog signal is to be converted into a digital signal using the analog input channel
specification register (ADS).
<2> The sample & hold circuit samples the voltage input to the selected analog input channel.
<3> After sampling for a specific time, the sample & hold circuit enters the hold status and holds the input analog
voltage until it has been converted into a digital signal.
<4> Set bit 9 of the successive approximation register (SAR). The tap selector sets the voltage tap of the series
resistor string to (1/2)AV
REF0
.
<5> The voltage comparator compares the voltage difference between the voltage tap of the series resistor string
and the analog input voltage. If the analog input voltage is greater than (1/2)AV
REF0
, the MSB of the SAR
remains set. If the analog input voltage is less than the (1/2)AV
REF0
, the MSB is reset.
<6> Next, bit 8 of SAR is automatically set and the next comparison starts. Depending on the value of bit 9 to
which the result of the preceding comparison has been set, the voltage tap of the series resistor string is
selected as follows.
Bit 9 = 1: (3/4)AV
REF0
Bit 9 = 0: (1/4)AV
REF0
The analog input voltage is compared with one of these voltage taps and bit 8 of SAR is manipulated as
follows depending on the result of the comparison.
Analog input voltage
≥
voltage tap: bit 8 = 1
Analog input voltage
≤
voltage tap: bit 8 = 0
<7> The above steps are repeated until bit 0 of SAR has been manipulated.
<8> When comparison of all 10 bits of SAR has been completed, the valid digital value remains in SAR, and the
value of SAR is transferred and latched to the A/D conversion result register (ADCR).
At the same time, an A/D conversion end interrupt request (INTAD) can be generated.
Caution
The first conversion value immediately following the start of A/D conversion may not satisfy
the ratings.