UPD78F0411GA-GAM-AX Datasheet, PDF (304/564 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 12 10-BIT SUCCESSIVE APPROXIMATION TYPE A/D CONVERTER (μPD78F041x only)
12.4 10-Bit Successive Approximation Type A/D Converter Operations
12.4.1 Basic operations of A/D converter
<1> Set bit 0 (ADCE) of the A/D converter mode register (ADM) to 1 to start the operation of the comparator.
<2> Set channels for A/D conversion to analog input by using the A/D port configuration register (ADPC0) and set
to input mode by using port mode register 2 (PM2).
<3> Set A/D conversion time by using bits 6 to 1 (FR3 to FR0, LV1, and LV0) of ADM.
<4> Select one channel for A/D conversion using the analog input channel specification register (ADS).
<5> Start the conversion operation by setting bit 7 (ADCS) of ADM to 1.
(<6> to <12> are operations performed by hardware.)
<6> The voltage input to the selected analog input channel is sampled by the sample & hold circuit.
<7> 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.
<8> Bit 9 of the successive approximation register (SAR) is set. The series resistor string voltage tap is set to
(1/2) AVREF by the tap selector.
<9> 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) AVREF, the MSB of SAR remains set to 1. If the
analog input is smaller than (1/2) AVREF, the MSB is reset to 0.
<10> 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) AVREF
• Bit 9 = 0: (1/4) AVREF
The voltage tap and sampled 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
<11> Comparison is continued in this way up to bit 0 of SAR.
<12> 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.
<13> Repeat steps <6> to <12>, 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 <5>. To start A/D conversion again when
ADCE = 0, set ADCE to 1, wait for 1 μs or longer, and start <5>. To change a channel of A/D conversion,
start from <4>.
Caution Make sure the period of <1> to <5> is 1 μs or more.
Remark
Two types of A/D conversion result registers are available.
• ADCR (16 bits): Store 10-bit A/D conversion value
• ADCRH (8 bits): Store 8-bit A/D conversion value
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User’s Manual U18698EJ1V0UD