UPD17P136ACT datasheet(148/292 Pages) NEC

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CHAPTER 13 PERIPHERAL HARDWARE

129

13.3.2 Functions of A/D Converter

(1) ADC0 – ADC3

These pins are used to input 4-channel analog voltage to the A/D converter. The A/D converter contains a

sample hold circuit. Analog input voltage is internally retained during A/D conversion.

(2) VADC

This pin is used to input the power supply and the reference voltage for the A/D converter.

A signal input to ADC0 to ADC3 is converted to a digital signal based on voltage applied across VADC and GND.

To reduce the current consumption of the microcontroller, the A/D converter has a function for automatically

stopping the current which flows into the VADC pin when the converter is not operating. Current flows into the

VADC pin in the following cases.

<1> Successive mode (ADCSOFT=0)

From when the ADCSTRT flag is set (1) until the ADCEND flag is set (1).

<2> Single mode (ADCSOFT=1)

From when the ADCSTRT flag is set (1) or from when a value of the 8-bit data register is written until

the result of comparison by the comparator is written in the ADCCMP flag.

Caution If the HALT Instruction is executed while the A/D conversion is in progress, the A/D

converter stops conversion. Note that, in this case, the HALT mode is set with current

flowing to the VADC pin. When the HALT mode has been released, the A/D conversion

is resumed. At this time, however, the value of ADCR is undefined, and the correct

conversion result cannot be obtained.

Remark

A/D conversion is stopped if the STOP instruction is executed while the conversion is in

progress. In this case, the A/D converter is initialized, and the current to the VADC pin is also

cut. The A/D converter remains stopped even if the STOP mode has been released.

(3) 8-bit data register (ADCR)

In the successive mode, this 8-bit data register stores A/D conversion results for successive approximation.

It is read by the GET instruction. In the single mode, the data in this register is converted to analog voltage

by the internal D/A converter and the comparator compares this voltage with an analog signal input from the

ADCn pin. A value can be written in this register by using the PUT instruction.

(4) Comparator

The comparator compares an analog input voltage from a pin with voltage output from the D/A converter. Value

1 is output if analog input voltage from the pin is high. Value 0 is output if this voltage is low. The comparison

result is stored in the 8-bit data register (ADCR) in the successive mode. It is stored in the ADCCMP flag in

the single mode.

(5) A/D converter control register

Figure 13-14 shows the A/D converter control register.

UPD17P136ACT Datasheet(PDF) 148 Page - NEC