Vi điều khiển và ứng dụng ADC

Các bước khởi động ADCConfigure the A/D module configure the port pins as analogue inputs, voltage reference, and digital I/O pins, select A/D converter input channel, select A/D co

Chuyên đề II

Vi điều khiển và ứng dụng

Ví dụ về ADC

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Conversion time

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Mạch ứng dụng

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To help designing analog hardware filters, Microchip offers a small application named FilterLab

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A/D block

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Các bước khởi động ADC

Configure the A/D module

configure the port pins as analogue inputs, voltage reference, and digital I/O pins,

select A/D converter input channel,

select A/D conversion clock,

select A/D conversion trigger source,

turn on A/D module;

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Configure A/D interrupt (if required)

clear ADIF bit (IFS0,11>),

select A/D interrupt priority,

set ADIE bit (IEC0<11>);

Start sampling

Wait the required acquisition time;

Trigger acquisition end, start conversion;

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Wait for A/D to complete, by either

waiting for the A/D interrupt, or

waiting for the DONE bit to get set;

Read A/D result buffer, clear ADIF bit if required.

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Voltage reference

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Acquisition / Conversion Timing

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Chọn kênh

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Manual Acquisition / Conversion

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Setting A/D Conversion Time

ADCS sets conversion clock period

D

 Related to clock used by processor

Tcy = 1 / MIPS

Tconv = Desired conversion time

Clocks per conversion = 14 for 12-bit A/D

 ADCS = ((2 * Tconv) / (14 * Tcy)) - 1

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Ví dụ

 ADCS = ((2 * Tconv) / (CConv * Tcy)) - 1

Example: 30 MIPS device, 12-bit A/D, max rate

 Tcy = 1 / 30 MIPS = 33.3 nsec

 Tconv = 10 mSec (min) by specification

ADCS = ((2 * 10*10-6) / (14 * 33.3*10-9)) – 1

= 41.8

 ADCS = 42 = 0x24 = 0b101010

Tad = (ADCS+1) * (Tcy/2) = 716 nsec

Tconv = 14 * Tad= 10.03 mSec

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Internal AD RC clock

ADRC enables internal AD RC clock

 ADCS bits are ignored

 For 12-bit A/D

 Nominal Rate = 47 KSPS Nominal Tconv = 21 mSec

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Chu kỳ ADC

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Ví dụ lấy mẫu và chuyển đổi thủ công

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Ví dụ về khởi động bằng timer ngoài

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C sample

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Buffer will reset to

ADCBUF0 after each

Interrupt

User software has

read only access to buffer

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Buffer Data Formats

Results presented in one of four formats

Channel Scanning

When (CSCNA = 1) group A will scan analog inputs

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AD1CON2 = 0; // use MUXA, AVss and AVdd are used as AD1CON3 = 0x1F02; // Tad = 2 x Tcy = 125ns >75ns

Vref+/-AD1CON1bits.ADON = 1; // turn on the ADC

while (TMR1< 100); // 6.25 us AD1CON1bits.DONE = 1; // 4 start the conversion while (!AD1CON1bits.DONE); // 5 wait for the conversion to complete return ADC1BUF0; // 6 read the conversion result

} // readADC

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AD1CON2 = 0; // use MUXA, AVss and AVdd are used as AD1CON3 = 0x1F02; // Tsamp = 32 x Tad; Tad=125ns

Vref+/-AD1CON1bits.ADON = 1; // turn on the ADC } //initADC

int readADC( int ch)

{

AD1CHS = ch; // 1 select analog input channel AD1CON1bits.SAMP = 1; // 2 start sampling while (!AD1CON1bits.DONE); // 3 wait for the conversion to complete return ADC1BUF0; // 4 read the conversion result

} // readADC

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