CHAPTER 13 A/D CONVERTER
Page 303 of 920
13.4
A/D Converter Conversion Operations
The A/D converter conversion operations are described below.
<1> The voltage input to the selected analog input channel is sampled by the sample & hold circuit.
<2> When sampling has been done for a certain time, the sample & hold circuit is placed in the hold state and the
sampled voltage is held until the A/D conversion operation has ended.
<3> Bit 9 of the successive approximation register (SAR) is set. The series resistor string voltage tap is set to (1/2)
AV
REF
by the tap selector.
<4> The voltage difference between the series resistor string voltage tap and sampled voltage is compared by the
voltage comparator. If the analog input is greater than (1/2) AV
REF
, the MSB bit of the SAR register remains set
to 1. If the analog input is smaller than (1/2) AV
REF
, the MSB bit is reset to 0.
<5> Next, bit 8 of the SAR register 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
REF
• Bit 9 = 0: (1/4) AV
REF
The voltage tap and sampled voltage are compared and bit 8 of the SAR register is manipulated as follows.
• Sampled voltage
≥
Voltage tap: Bit 8 = 1
• Sampled voltage < Voltage tap: Bit 8 = 0
<6> Comparison is continued in this way up to bit 0 of the SAR register.
<7> Upon completion of the comparison of 10 bits, an effective digital result value remains in the SAR register, 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.
<8> Repeat steps <1> to <7>, until the ADCS bit is cleared to 0
To stop the A/D converter, clear the ADCS bit to 0.
Note 1.
If the A/D conversion result is outside the A/D conversion result range specified by the ADRCK bit and
the ADUL and ADLL registers (see
), the A/D conversion result interrupt request signal is
not generated and no A/D conversion results are stored in the ADCR and ADCRH registers.
Note 2.
While in the sequential conversion mode, the ADCS flag is not automatically cleared to 0. This flag is not
automatically cleared to 0 while in the one-shot conversion mode of the hardware trigger no-wait mode,
either. Instead, 1 is retained.
Remark 1.
Two types of the A/D conversion result registers are available.
• ADCR register (16 bits): Store 10-bit A/D conversion value
• ADCRH register (8 bits): Store 8-bit A/D conversion value
Remark 2.
AV
REF
: The + side reference voltage of the A/D converter. This can be selected from AV
REFP
and V
DD
.
Summary of Contents for RL78/G1H
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