10-Bit A/D Converter Operation; Basic Operation Of 10-Bit A/D Converter - NEC mPD789101 User Manual

CHAPTER 12 10-BIT A/D CONVERTER ( µ PD789114, 789134 SUBSERIES)

12.4 10-Bit A/D Converter Operation

12.4.1 Basic operation of 10-bit A/D converter

<1> Select a channel for A/D conversion, using A/D input select register 0 (ADS0).
<2> The voltage supplied to the selected analog input channel is sampled using the sample and hold circuit.
<3> After sampling continues for a certain period of time, the sample and hold circuit is put on hold to keep
the input analog voltage until A/D conversion is completed.
<4> Bit 9 of the successive approximation A/D conversion register (SAR) is set. The series resistor string
voltage tap at the tap selector is set to half of AV
<5> The series resistor string tap voltage is compared with the analog input voltage using the voltage
comparator. If the analog input voltage is higher than half of AV
is lower than half of AV
<6> Bit 8 of the SAR is set automatically, and comparison shifts to the next stage. The next voltage tap of
the series resistor string is selected according to bit 9, which reflects the previous comparison result, as
follows:
• Bit 9 = 1: Three quarters of AV
• Bit 9 = 0: One quarter of AV
The tap voltage is compared with the analog input voltage. Bit 8 is set or reset according to the result
of comparison.
• Analog input voltage ≥ tap voltage: Bit 8 = 1
• Analog input voltage < tap voltage: Bit 8 = 0
<7> Comparison is repeated until bit 0 of the SAR is reached.
<8> When comparison is completed for all of the 10 bits, a significant digital result is left in the SAR. This
value is sent to and latched in A/D conversion result register 0 (ADCR0). At the same time, it is possible
to generate an A/D conversion end interrupt request (INTAD0).
Cautions 1. The A/D conversion value immediately after starting the A/D conversion operation may
be undefined.
2. When in standby mode, the A/D converter stops operation.
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, the MSB is reset.
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User's Manual U13045EJ2V0UM00
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, the MSB of the SAR is left set. If it
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