Operation; Basic Operation - NEC V850/SA1 mPD703015 Preliminary User's Manual

11.4 Operation

11.4.1 Basic operation

<1> Select one channel whose analog signal is to be converted into a digital signal by 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 the bit 9 of the successive approximation register (SAR). The tap selector sets the voltage tap of the
series resistor string to (1/2)AV
<5> The voltage difference between the voltage tap of the series resistor string and the analog input voltage is
compared by the voltage comparator. If the analog input voltage is greater than (1/2)AV
SAR remains set. If the analog input voltage is less than (1/2)AV
<6> Next, bit 8 of the SAR is automatically set, and the analog input voltage is compared again. 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
•
Bit 9 = 0: (1/4)AV
The analog input voltage is compared with one of these voltage taps, and bit 8 of the 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 the bit 0 of the SAR has been manipulated.
<8> When comparison of all the 10 bits of the SAR has been completed, the valid digital value remains in the
SAR, and the value of the 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 value of the first A/D conversion may not satisfy the ratings immediately after the start of
A/D conversion.
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CHAPTER 11
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REF
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A/D CONVERTER
, the MSB is reset.
REF
, the MSB of the
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