UPD78F1502AGK-GAK-AX Datasheet, PDF (453/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 13 VOLTAGE REFERENCE (μ PD78F150xA only)
Cautions 3. Rewriting DACSWn (n = 0, 1) during A/D conversion is prohibited when both the positive
reference voltage of the A/D converter (ADREFP) and the positive reference voltage of the D/A
converter (DAREFP) are the voltage reference output (VREFOUT) (VRSEL = 1 and DAREF = 1).
Rewrite it when conversion operation is stopped (ADCS = 0).
4. Do not change the output voltage of the reference voltage by using VRGV during the voltage
reference operation (VRON = 1).
13.4 Voltage Reference Operations
The voltage reference has the following mode.
• Reference voltage output mode
A reference voltage is output from the VREFOUT pin. Furthermore, the generated reference voltage is supplied to the
internal A/D and D/A converters. 2.0 V (TYP.) or 2.5 V (TYP.) can be selected as the output voltage.
13.4.1 Reference voltage output mode
The procedure for starting operation is described below.
<1> Set bit 5 (ADCEN) of peripheral enable register 0 (PER0) to 1 to start the supply of the input clock to the voltage
reference.
<2> Set bit 3 (VRSEL) of the analog reference voltage control register (ADVRC) to 1. The positive reference voltage of
both the A/D and D/A converters or only the A/D converter is set to voltage reference output.
<3> Specify the reference voltage value by using bit 1 (VRGV) of ADVRC.
<4> Enable voltage reference operation by setting bit 0 (VRON) of ADVRC to 1.
<5> Use software to wait until the voltage reference operation stabilizes (settling time: 17 ms (max.)).
13.5 Cautions for Voltage Reference
Observe the following cautions when using the voltage reference.
• The VREFOUT output voltage can be used only as the positive reference voltage of the internal A/D and D/A converters
of the microcontroller. Do not connect an external circuit other than a tantalum capacitor (capacitance: 10 μF±30 %,
ESR: 2 Ω (max.), ESL: 10 nH (max.)) and a ceramic capacitor (capacitance: 0.1 μF±30 %, ESR: 2 Ω (max.), ESL: 10
nH (max.)) to the VREFOUT pin for stabilizing the reference voltage.
R01UH0004EJ0501 Rev.5.01
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Jun 20, 2011