A/D Converter Operations; Basic Operations Of A/D Converter - NEC 78K0S/KA1+ Preliminary User's Manual

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10.4 A/D Converter Operations

10.4.1 Basic operations of A/D converter

<1> Select one channel for A/D conversion using the analog input channel specification register (ADS).
<2> Set ADCE to 1 and wait for 1
<3> Set ADCS to 1 and start the conversion operation.
(<4> to <10> are operations performed by hardware.)
<4> The voltage input to the selected analog input channel is sampled by the sample & hold circuit.
<5> When sampling has been done for a certain time, the sample & hold circuit is placed in the hold state and the
input analog voltage is held until the A/D conversion operation has ended.
<6> Bit 9 of the successive approximation register (SAR) is set. The series resistor string voltage tap is set to
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(1/2) AV
<7> The voltage difference between the series resistor string voltage tap and analog input is compared by the
voltage comparator. If the analog input is greater than (1/2) AV
analog input is smaller than (1/2) AV
<8> Next, bit 8 of SAR is automatically set to 1, and the operation proceeds to the next comparison. The series
resistor string voltage tap is selected according to the preset value of bit 9, as described below.
• Bit 9 = 1: (3/4) AV
• Bit 9 = 0: (1/4) AV
The voltage tap and analog input voltage are compared and bit 8 of SAR is manipulated as follows.
• Analog input voltage ≥ Voltage tap: Bit 8 = 1
• Analog input voltage < Voltage tap: Bit 8 = 0
<9> Comparison is continued in this way up to bit 0 of SAR.
<10> Upon completion of the comparison of 10 bits, an effective digital result value remains in SAR, and the result
value is transferred to the A/D conversion result register (ADCR, ADCRH) and then latched.
At the same time, the A/D conversion end interrupt request (INTAD) can also be generated.
<11> Repeat steps <4> to <10>, until ADCS is cleared to 0.
To stop the A/D converter, clear ADCS to 0.
To restart A/D conversion from the status of ADCE = 1, start from <3>. To restart A/D conversion from the
status of ADCE = 0, however, start from <2>.
Remark The following two types of A/D conversion result registers can be used.
<1> ADCR (16 bits): Stores a 10-bit A/D conversion value.
<2> ADCRH (8 bits): Stores an 8-bit A/D conversion value.
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CHAPTER 10 A/D CONVERTER
µ
s or longer.
by the tap selector.
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Preliminary User's Manual U16898EJ1V0UD
, the MSB of SAR remains set to 1. If the
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, the MSB is reset to 0.