7630 datasheet(159/238 Pages) RENESAS

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2-93

7630 Group User’s Manual

APPLICATION

2.6 A-D converter

Fig. 2.6.6 Control procedure [Measurement of analog signals]

ADCON [Address: 001516]

XXX110012

ADCON [Address: 001516], bit 3?

• Check the completion of A-D conversion

with the A-D conversion completion bit.

P0D [Address: 000916]

XXXXXX0X2

ADCON [Address: 001516], bit 3

Read out AD [Address: 001416]

X : These bits are not used in this application.

Please set these bits to “0” or “1” appropriately.

• Select the P01/AN1 pin as an analog input pin.

• P01/AN1 pin : Input mode

• Start A-D conversion.

• Read out the conversion result.

The A-D conversion completion bit is cleared to “0” at this reading.

Control procedure : By setting the related registers as shown in Figure 2.6.6, the analog voltage

input from the sensor are converted into digital values.

2.6.4 Conversion time

On A-D conversion process takes 53 to 54 cycles of the internal system clock

φ.

2.6.5 Notes on use

(1) Analog input pin

Make the signal source impedance for analog input low, or equip an analog input pin with an external

capacitor of 0.01

µF to 1µF. Further, be sure to verify the operation of application products on the user

side.

Reason

An analog input pin includes the capacitor for analog voltage comparison. Accordingly, when signals

from signal source with high impedance are input to an analog input pin, charge and discharge noise

generates. This may cause the A-D conversion precision to be worse.

(2) Reference voltage input pin (VREF)

Apply a voltage of 2V to VCC to the reference voltage input pin VREF during A-D conversion. Note that

if the reference voltage is lowered below the above value, the A-D conversion precision will be

degraded.

(3) Oscillation frequency during A-D conversion

The comparator is configured by capacity coupling, so the charge is lost if the clock input oscillation

frequency is low. Set f(XIN) at 500kHz or more during A-D conversion.

(4) Set the analog input pin to input mode

Clear the bit of the Port P0 direction register [Address: 000916] which correponds to the used analog

input pin to “0” (input mode).

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