
CHAPTER 14 A/D CONVERTER
User’s Manual U16890EJ1V0UD
421
14.4 Operation
14.4.1 Basic operation
<1> Select the channel whose analog signal is to be converted into a digital signal using the ADS register.
<2> Set (1) the ADM.ADCS2 bit and wait 17
μ
s (14
μ
s when AV
REF0
≥
4.0 V) or longer.
<3> Set the ADM.ADCS bit to 1 to start A/D conversion.
(Steps <4> to <10> are executed by hardware.)
<4> The sample & hold circuit samples the voltage input to the selected analog input channel.
<5> 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.
<6> 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
.
<7> 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
register remains set. If the analog input voltage is less than (1/2)
×
AV
REF0
, the MSB is reset.
<8> Next, bit 8 of the SAR register 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 the SAR register 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
<9> The above steps are repeated until bit 0 of the SAR register has been manipulated.
<10> When comparison of all 10 bits of the SAR register has been completed, the valid digital value remains in the
SAR register, and the value of the SAR register is transferred and latched to the ADCR register.
At the same time, an A/D conversion end interrupt request signal (INTAD) is generated.
<11> Repeat steps <4> to <10> until the ADCS bit is cleared to 0.
For another A/D conversion, start at <3>. However, when operating the A/D converter with the ADCS2 bit
cleared to 0, start at <2>.