HT67F60 datasheet(157/242 Pages) HOLTEK

157 / 242 page

HT67F30/HT67F40/HT67F50/HT67F60

TinyPowerTM A/D Flash Type 8-Bit MCU with LCD & EEPROM

Rev. 1.50

156

March 06 , 2012

Rev. 1.50

157

March 06 , 2012

The accompanying diagram shows graphically the various stages involved in an analog to digital

conversion process and its associated timing. After an A/D conversion process has been initiated by

the application program, the microcontroller internal hardware will begin to carry out the

conversion, during which time the program can continue with other functions. The time taken for the

A/D conversion is 16tADCK where tADCK is equal to the A/D clock period.

Programming Considerations

During microcontroller operations where the A/D converter is not being used, the A/D internal

circuitry can be switched off to reduce power consumption, by setting bit ADOFF high in the

ADCR0 register. When this happens, the internal A/D converter circuits will not consume power

irrespective of what analog voltage is applied to their input lines. If the A/D converter input lines are

used as normal I/Os, then care must be taken as if the input voltage is not at a valid logic level, then

this may lead to some increase in power consumption.

A/D Transfer Function

As the devices contain a 12-bit A/D converter, its full-scale converted digitised value is equal to

FFFH. Since the full-scale analog input value is equal to the VDD or VREF voltage, this gives a single

bit analog input value of VDD or VREF divided by 4096.

1LSB=(VDDorVREF) ÷ 4096

The A/D Converter input voltage value can be calculated using the following equation:

A/D input voltage =

A/Doutputdigitalvalue×(VDDorVREF) ÷ 4096

The diagram shows the ideal transfer function between the analog input value and the digitised

output value for the A/D converter. Except for the digitised zero value, the subsequent digitised

values will change at a point 0.5 LSB below where they would change without the offset, and the

last full scale digitised value will change at a point 1.5 LSB below the VDD or VREF level.

A/D Programming Example

The following two programming examples illustrate how to setup and implement an A/D

conversion. In the first example, the method of polling the EOCB bit in the ADCR0 register is used

to detect when the conversion cycle is complete, whereas in the second example, the A/D interrupt is

used to determine when the conversion is complete.

FF EH

(

)

A/ D C onv er si on

Re su lt

FFFH

FF DH

03H

02H

01H

0. 5 LS B

409 3 4094 4095 409 6

A nal og In pu t Vo lt age

1. 5 LS B

V DD or V RE F

409 6

Ideal A/D Transfer Function

HT67F60 Datasheet(PDF) 157 Page - Holtek Semiconductor Inc

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