Chuyên đề II Vi điều khiển ứng dụng ADC Ví dụ về ADC Conversion time Mạch ứng dụng To help designing analog hardware filters, Microchip offers a small application named FilterLab A/D  12-bit/10bit Resolution with +/- 1-bit accuracy  100 K Samples / Sec conversion rate  Sample/Hold Amplifier  Up to 16 Analog Inputs  Analog Input Range: (VREF-) to  Multiple conversion trigger sources (VREF+) Hardware A/D block Các bước khởi động ADC  Configure theA/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; Tiếp  ConfigureA/D interrupt (if required)  clear ADIF bit (IFS0,11>),  select A/D interrupt priority,  set ADIE bit (IEC0);  Start sampling  Wait the required acquisition time;  Trigger acquisition end, start conversion; Tiếp  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 10 Acquisition / Conversion Timing 12 Chọn kênh 13 Manual Acquisition / Conversion 14 Setting A/D Conversion Time  ADCS sets conversion clock period   ADCS value limited by maximum SPS of A/D Related to clock used by processor  Tcy =1 / MIPS  Tconv =Desired conversion time  Clocks per conversion =14 for 12-bit A/D  15 ADCS =((2 * Tconv) / (14 * Tcy)) - Ví dụ  ADCS =((2 * Tconv) / (CConv * Tcy)) - 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)) – =41.8  ADCS =42 =0x24 =0b101010  Tad =(ADCS+1) * (Tcy/2) =716 nsec  Tconv =14 * Tad=10.03 mSec 16 Internal AD RC clock  ADRC enables internal AD RC clock  ADCS bits are ignored   17 For 12-bit A/D Nominal Rate =47 KSPS Nominal Tconv =21 mSec Chu kỳ ADC 18 Ví dụ lấy mẫu chuyển đổi thủ công 19 Ví dụ khởi động timer 20 C sample 21 A/D Buffer  Module has a 16-word buffer  Module writes results into buffer in completion  Buffer will reset to ADCBUF0 after each Interrupt  User software has read only access to buffer 22 Buffer Data Formats  Results presented in one of four formats  Integer (DOUT =0000 dddd dddd dddd)  Fractional (DOUT =dddd dddd dddd 0000)  Signed Integer (DOUT =ssss sddd dddd dddd)  Signed fractional (DOUT =sddd dddd dddd 0000) 23 Channel Scanning  When (CSCNA =1) group A will scan analog inputs 24 C examples void initADC( int amask) { AD1PCFG =amask; // select analog input pins AD1CON1 =0; // manual conversion sequence control AD1CSSL =0; // no scanning required AD1CON2 =0; // use MUXA, AVss and AVdd are used as Vref+/AD1CON3 =0x1F02; // Tad =2 x Tcy =125ns >75ns AD1CON1bits.ADON =1; // turn on theADC } //initADC int readADC( int ch) { AD1CHS =ch; // select analog input channel AD1CON1bits.SAMP =1; // start sampling TMR1 =0; // wait for sampling time while (TMR1[...]... 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 16 Internal AD RC clock  ADRC enables internal AD RC clock  ADCS bits are ignored   17 For 12-bit A/D Nominal Rate =47 KSPS Nominal Tconv =21 mSec Chu kỳ ADC 18 Ví dụ lấy mẫu và chuyển đổi thủ công 19 Ví dụ về khởi... Conversion 14 Setting A/D Conversion Time  ADCS sets conversion clock period   ADCS value limited by maximum SPS of A/D Related to clock used by processor  Tcy =1 / MIPS  Tconv =Desired conversion time  Clocks per conversion =14 for 12-bit A/D  15 ADCS =((2 * Tconv) / (14 * Tcy)) - 1 Ví dụ  ADCS =((2 * Tconv) / (CConv * Tcy)) - 1 Example: 30 MIPS device, 12-bit A/D, max rate  Tcy =1 / 30 MIPS... will scan analog inputs 24 C examples void initADC( int amask) { AD1PCFG =amask; // select analog input pins AD1CON1 =0; // manual conversion sequence control AD1CSSL =0; // no scanning required AD1CON2 =0; // use MUXA, AVss and AVdd are used as Vref+/AD1CON3 =0x1F02; // Tad =2 x Tcy =125ns >75ns AD1CON1bits.ADON =1; // turn on theADC } //initADC int readADC( int ch) { AD1CHS =ch; // 1 select analog... return ADC1 BUF0; // 6 read the conversion result } // readADC 25 Automatic sampling timing void initADC( int amask) { AD1PCFG =amask; // select analog input pins AD1CON1 =0x00E0; // automatic conversion start after sampling AD1CSSL =0; // no scanning required AD1CON2 =0; // use MUXA, AVss and AVdd are used as Vref+/AD1CON3 =0x1F02; // Tsamp =32 x Tad; Tad=125ns AD1CON1bits.ADON =1; // turn on theADC }... =0x1F02; // Tsamp =32 x Tad; Tad=125ns AD1CON1bits.ADON =1; // turn on theADC } //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 ADC1 BUF0; // 4 read the conversion result } // readADC 26 ... dụ lấy mẫu và chuyển đổi thủ công 19 Ví dụ về khởi động bằng timer ngoài 20 C sample 21 A/D Buffer  Module has a 16-word buffer  Module writes results into buffer in completion  Buffer will reset to ADCBUF0 after each Interrupt  User software has read only access to buffer 22 Buffer Data Formats  Results presented in one of four formats  Integer (DOUT =0000 dddd dddd dddd)  Fractional (DOUT =dddd ... =33.3 nsec  Tconv =10 mSec (min) by specification  ADCS =((2 * 10*10-6) / (14 * 33.3*10-9)) – =41.8  ADCS =42 =0x24 =0b101010  Tad =(ADCS+1) * (Tcy/2) =716 nsec  Tconv =14 * Tad=10.03 mSec... Vref+/AD1CON3 =0x1F02; // Tad =2 x Tcy =125ns >75ns AD1CON1bits.ADON =1; // turn on theADC } //initADC int readADC( int ch) { AD1CHS =ch; // select analog input channel AD1CON1bits.SAMP =1; // start... (!AD1CON1bits.DONE); // wait for the conversion to complete return ADC1 BUF0; // read the conversion result } // readADC 25 Automatic sampling timing void initADC( int amask) { AD1PCFG =amask; // select analog