04 adc (pic24, ds pic with dma)

1
Analog-to-Digital Conversion
(PIC24, dsPIC with DMA)
Industrial Embedded Systems

2
 ADC architectures
 Steps of A/D conversion
 Configure A/D module of PIC24
 A/D Interrupt
 Using multiple channels
 dsPIC utilizing DMA
Outline

3
 Successice Approximation Register
 AD Converter with feedback
 Generally N=8-16 bit (PIC24FJ128GA010 has N=10bit ADC)
 Conversion time: N cycle
Initially set VDAC to ½ Vref, then see if Vin higher or lower than VDAC. If >
½ Vref, then next guess is between Vref and ½Vref, else next guess is
between Vref and GND. Do this for each bit of the ADC
ADC architectures
SAR

4
Counter ramp ADC
 Simple
 Slow
 Conversion time: 2N cycle
 Fast
 Conversion time: 1 cycle
 Requires the most transistors of any
architecture, N-bit converter requires 2N-1
comparators.
 Commercially available flash converters
up to 12 bits.
Flash ADC
ADC architectures

5Industrial Embedded Systems
Input hardware for ADC
 Some low-pass filtering and
a Zener diode to protect the
input PIN from overvoltage
 If input voltage is
higher, a voltage divider
can be used to fit the
voltage level.
 To improve the
performance a voltage
follower is also applied (use
a rail-to-rail Op-Amp)

6
 Configuring AD modul
 Enable analog input channel(s)
 Set the reference voltage
 Clock cycle, clock source (TAD)
 Sampling and conversion settings
 Form of the result
 Enable modul
 Configure A/D interrupt (if required)
 Delete flag belonging to the ADC
 Enable interrupt
 Select the given analog channel
 Sampling time (1-31 TAD)
 Time to charge up the storage capacitor
 Conversion time (12 TAD)
 The end of the conversion is indicated by a flag
 Read the value from the buffer register
 If required delete interrupt flag
Steps of AD conversion

7
 AD module has 6 Special Function Register (SFR)
 AD1CON1, AD1CON2, AD1CON3, AD1CHS, AD1PCFG, AD1CSSL
 PIC24 has 16 analog input pin (AN0-AN15)
 Enable analog input channel(s)
 Using AD1PCFG register
 0s will mark the analog inputs, and 1s will configure the respective
pins as digital inputs
 AD1PCFG = 0xFFDF; // AN5 analog input
 Set the reference voltage
 AD1CON2 register<15:13>
 Internal voltage level (AVDD, AVSS)
 External reference voltage
 Combination of the two
 AD1CON2bits.VCFG = 0b000; // ref+=VDD, ref-=VSS
Configure AD modul

8
 Clock cycle (TAD)
 In the case of PIC24FJ128GA010 minimum clock cylce TAD is 75ns
 Clock derived from sytem clock (TCY)
 AD1CON3bits.ARDC = 0; //system clock, TCY=2*TOSC
 TAD=TCY (ACDS + 1)
 AD1CON3bits.ADCS = 0; //TAD=TCY=250ns>75ns
Configure AD modul

9
 Sampling time
 Its value depends on the input resistane of the signal and the storage
capacitor
 The frequency of the input signals also has to be taken into consideration
 The accuracy can be improved by increasing the sampling time
Configure AD modul

10
 Sampling and conversion settings
 The sampling time and the beginning of the conversion can be determined
 By software (delete AD1CON1bits.SAMP bit)
 By hardware (Active transition on INT0 pin ends sampling and starts
conversion)
 Automatic conversion
 AD1CON3bits.SSRC = 0b000; //software conversion
 AD1CON3bits.SSRC = 0b111; //automatic conversion
 In the case of software conversion the enough sampling time should be
guaranteed in the code
 In the case of automatic conversion the sampling has to set:
 AD1CON1bits.SAMC = 31; //TSAMP=31TAD=7.75us
 After conversion automatically
 Sampling begins immediately after last conversion completes
 Sampling begins when SAMP bit is set
 AD1CON1.ASAM = 0; //no automatic sampling
Configure AD modul

11
 Data output format
 integer/fractional and signed/nonsigned
 AD1CON1bits.FORM = 0b00; //integer
 PIC put the result of the AD conversion in to a 16-bit register
ADC1BUF x
 Enable the module
 AD1CON1bits.ADON = 1; //turn on ADC
Configure AD modul

12
void initADC()
{
AD1PCFG = 0xFFDF; // enable AN5 chnnel
AD1CON1bits.SSRC = 0b000; //software conversion
AD1CON1bits.FORM = 0b00; //integer
AD1CON2bits.VCFG = 0b000; // ref+=VDD, ref-=VSS
AD1CON3bits.ADRC = 0; //system clock, TCY=2*TOSC
AD1CON3bits.ADCS = 0; //TAD=TCY=250ns>75ns
AD1CON1bits.ADON = 1; //turn on ADC
}
Configure AD modul

13
 Potenciometer  Temperature sensor
 Select the input channel
 AD1CHS.CH0SA = 5; //selecting AN5 (potenciometer)
Analog inputs on demo board

14
#include <p24fj128ga010.h>
_CONFIG1( JTAGEN_OFF & FWDTEN_OFF )
_CONFIG2( POSCMOD_HS & FNOSC_PRI )
void initADC(); // declaration of ADC initialization
void initT1(); //declaration of Timer1 initialization
int main ( void )
{
initADC(); // call ADC init
initT1(); // call Timer1 init
TRISA = 0xFF00; // PORTA lower 8 bit output
LATA = 0x0000; // delete PORTA
while(1) //infinite loop
{
AD1CHSbits.CH0SA=5; //select AN5 (potentiometer)
AD1CON1bits.SAMP = 1; //start sampling
TMR1=0; //wait for sampling with software
while(TMR1<50);
AD1CON1bits.SAMP = 0; //end of sampling
AD1CON1bits.DONE = 1; //start conversion
while (!AD1CON1bits.DONE); //end of conversiom
LATA=(ADC1BUF0>>2); //put the 10bit result to the 8 LED
} //end of infinite loop
} //end of main loop
Example 1

15
void initADC() // define of ADC initialization
{
AD1CON1bits.SSRC = 0b000; //software conversion
}
void initT1() // define of Timer1 initialization
{
T1CONbits.TON = 1; //Timer1 turn on
T1CONbits.TCS = 0; //system clock =fosc/2
T1CONbits.TCKPS = 0b01; // prescaler 8
TMR1=0; //delete counter
}
Example 1

16
void initADC(); // AD inicializalo fv deklarálása
int main ( void )
{
initADC(); // call ADC init
while(1) //infinite loop
{
AD1CON1bits.SAMP = 1; //Start sampling (we do not need Timer1)
while (!AD1CON1bits.DONE); //end of conversion
LATA=(ADC1BUF0>>2); //put the 10bit result to the 8 LED
} //end of infinit loop
} //end of main loop
Example 2 (automatic conversion)

17
void initADC() // define ADC initialization
{
AD1CON1bits.SSRC = 0b111; //automatic conversion
AD1CON3bits.SAMC = 31; //Tsamp=31TAD
}
Example 2 (automatic conversion)

18
 Priority level
 IPC3bits.AD1IP
 Flag
 IFS0bits.AD1IF
 Enable bit
 IEC0bits.AD1IE
 We can select, after how many samling/conversion
 We can give after how many completion of sample/convert sequence an
interrupt occur
 AD1CON2bits.SMPI
 Interrupt function
void _ISR _ADC1Interrupt (void)
{
… //instruction
IFS0bits.AD1IF = 0; // delete ADC interrupt flag!!!
}
ADC interrupt

19
void initADC(); //declaration of ADC initialization
void _ISR _ADC1Interrupt (void); //declaration of interrupt function
int main ( void )
{
initADC(); // call ADC initialization
SRbits.IPL = 0; // priority level of processor
IPC3bits.AD1IP = 3; //priority level of ADC
IEC0bits.AD1IE = 1; //enable ADC interrupt
AD1CON1bits.SAMP = 1; //Start sampling (we do not need Timer1)
while(1); //infinite loop
}
Example 3 (automatic conversion + interrupt)

20
void _ISR _ADC1Interrupt (void)
{
LATA=(ADC1BUF0>>2); //instruction: put the result to the LED
IFS0bits.AD1IF = 0; //delete ADC interrupt flag
}
void initADC() // define of ADC initialization
{
AD1CON1bits.ASAM = 1; //after conversion automatically new sampling
AD1CON2bits.SMPI = 8; //interrupt after 8 sampling/conversion
}
Example 3 (automatic conversion + interrupt)

21
 To read multiple channel the „scan” instruction can be helpful, which put
the ADC value in different ADC1BUFx register
 To turn on scan:
 AD1CON2bits.CSCNA = 1;
 The required channels should be enabled in the AD1PCFG register
 In the AD1CSSL register we have to give the channels
 pl. AD1CSSL = 0x0030; //AN4 és AN5
 If we want to read the value of n channel, it is worth to make an interrupt
after n sampling/conversion sequence
 pl. AD1CON2bits.SMPI = 0b0001; //2 channels
 Read the value of the channels
 pl. value01 = ADC1BUF0; //AN4
value02 = ADC1BUF1; //AN5
 PIC fill up the ADC1BUFx register from x=0
Read multiple channel

22
void initADC()
{
AD1PCFG=0xFFCF; //AN4 and AN5
AD1CON1bits.ASAM = 1; //new sampling after conversion
AD1CON2bits.VCFG = 0b000; //ref+=VDD, ref-=VSS
AD1CON2bits.SMPI = 2; //interrupt after 2 AD conversion
AD1CON2bits.CSCNA = 1; //scan
AD1CON3bits.ADRC = 0; //TCY=2*TOSC
AD1CON1bits.ADON = 1; //ADC turn on
AD1CSSLbits.CSSL4=1; //include AN4 in the scan cycle
AD1CSSLbits.CSSL5=1; //include AN5 in the scan cycle
}
Example 4 (read multiple channel)

23
 Read the actual value of the temperature sensor and the poteniometer and
write their value in Celsius and Volt to the LCD display
Example 4 (read multiple channel)
void LCDFloat(float L,int length, unsigned int acc)
{
signed int intpart=(int) L;
if (intpart==0)
LCDNumber(intpart,1);
else
LCDNumber(intpart,-1);
putLCD('.');
int fraction, multi=1;
while(acc--)
{
multi*=10;
if(intpart>=0) //if positive
{
fraction=(L-(int)L)*multi;
}
else fraction=((int)L - L)*multi; //if negative
LCDNumber(fraction,1);
}
}

24
 ADC of dsPICs
 Up to 32 ADC input channel (100/121/144 pin device)
 10-bit ADC with four S&H block (simultaneous sampling, 1.1 Msps)
 12-bit ADC with one S&H block (500 ksps)
 DMA (Direct Memory Access) can be used
 DMA is an efficient mechanism of copying data between
peripheral SFRs and buffers or variables stored in RAM with
minimal CPU intervention
 If multiple conversions are done without DMA 16 registers named
ADCxBUF0-15 can be used for buffering the results and the ADC
interrupt is used to signal when a group of conversions is finished
 By using DMA, these registers are not present and DMA memory
is used to buffer the results and the DMA interrupt occuring when
a group of conversions has finished
Using dsPIC with DMA

25
DMA block diagram in dsPIC
 CPU communicates with conventional SRAM across the data space X-bus (modified
Hardvard architecture). It also communicates to port 1 of the dual port SRAM. It talks to
the peripherals acrosss a separate peripheral data space bus
 DMA communicates with port 2 of the dual port SRAM and the DMA port of each of the
DMA-ready peripheral across a dedicated transfer bus

26
DMA data transfer

27
Operating modes
 Moves a single block of data from a fixed (peripheral) address
 Alert CPU that the block is ready for processing
One-shot mode

28
Operating modes
 Moves multiple blocks of data to/from a fixed (peripheral) address
 Alert CPU that each block is ready for processing
 Automatically re-initializes DMA channel for the next block transfer
 Suitable for applications when CPU can stay ahead of CPU
Auto-repeat mode

29
Operating modes
 Alerts CPUwhen each block is half way through its total count
 Allows CPU time to start processing the buffer before it is overwritten
 Requires that the DMA data transfers stay ahead of CPU processing of
the buffer
Half Buffer transfer interrupt

30
Operating modes
 Moves multiple blocks of data to/from a fixed (peripheral) address
 Alert CPU that each block is ready for processing
 Automatically re-initializes DMA channel for next block transfer to an
alternate buffer (ping-pongs between 2 buffers)
 Allows CPU to process one buffer while the other fills/empties
Ping-Pong

31
Adressing mode
 Conventioanl DMA transfer moves the data into a sequential buffer
 The peripheral provides the address of DPSRAM address, the task of the
DMA to coordinate the data transfer and generate the CPU interrupts
 Scatter-gather addressing mode
PIA: Peripheral indirect addressing mode

32
 The presence of DMA requires the following:
 The ADC ISR (Interupt Service Routine) is no longer used. Now the
ADC interrupt occurs adter each conversion, at point the DMA
module transfers the results to a DMA buffer. The DMA interrupt is
used to do something with the ADC samples
 The DMA channel must be configured to be linked to the ADC module
and a buffer in DMA memory allocated for the ADC results
 There are two choices for storing the ADC results in DMA memory
 Conversion order
 Scatter/gather mode
DMA

33
 Configure oscillator of the dsPIC
Example 5 (ADC with DMA)
// Configure Oscillator to operate the device at 40Mhz
// Fosc= Fin*M/(N1*N2), Fcy=Fosc/2
// Fosc= 8M*40/(2*2)=80Mhz for 8M input clock
PLLFBD=38; // M=40
CLKDIVbits.PLLPOST=0; // N1=2
CLKDIVbits.PLLPRE=0; // N2=2
OSCTUN=0; // Tune FRC oscillator, if FRC is used
// Disable Watch Dog Timer
RCONbits.SWDTEN=0;
// Clock switch to incorporate PLL
__builtin_write_OSCCONH(0x03); // Initiate Clock Switch to Primary
// Oscillator with PLL (NOSC=0b011)
__builtin_write_OSCCONL(0x01); // Start clock switching
while (OSCCONbits.COSC != 0b011); // Wait for Clock switch to occur
// Wait for PLL to lock
while(OSCCONbits.LOCK!=1) {};

34
 Initialize ADC
void initADC(void)
{
AD1CON1bits.FORM = 0; // integer
AD1CON1bits.SSRC = 2; // Timer3 as sample clock source
AD1CON1bits.ASAM = 1; //auto sampling
AD1CON1bits.AD12B = 0; // 10-bit ADC operation
AD1CON1bits.SIMSAM = 1; //Simultaneous sampling
AD1CON2bits.CSCNA = 1; // Scan Inputs
AD1CON2bits.CHPS = 0;
AD1CON3bits.ADRC = 0; // ADC Clock is derived from Systems Clock
AD1CON3bits.ADCS = 63; // Tad=Tcy*(ADCS+1)= (1/40M)*64 = 1.6us (625Khz)
// ADC Conversion Time for 10-bit Tc=12*Tab = 19.2us
AD1CON1bits.ADDMABM = 0; //scatter/gather mode
AD1CON2bits.SMPI = 3; // 4 ADC Channel is scanned
AD1CON4bits.DMABL = 0b011; // Each buffer contains 8 words
AD1CSSH = 0x0000; //no scan for AN16-31
AD1CSSLbits.CSS4=1; // AN4 for scan

35
 Initialize ADC
//AD1PCFGH/AD1PCFGL: Port Configuration Register
AD1PCFGL=0xFFFF;
AD1PCFGH=0xFFFF;
AD1PCFGLbits.PCFG4 = 0; // AN4 analog input
IFS0bits.AD1IF = 0; // Clear the A/D interrupt flag bit
IEC0bits.AD1IE = 0; // Do Not Enable A/D interrupt
AD1CON1bits.ADON = 1; // Turn on the A/D converter
}

36
 Initialize DMA
void initDMA(void)
{
DMA0CONbits.AMODE = 0b10; // Peripheral indirect addressing mode
DMA0CONbits.MODE = 0b10; //Continuous Ping-Pong mode
DMA0PAD=(int)&ADC1BUF0; //contains the static address of the peripheral data register
DMA0CNT = 31; //8*4-1, the block transfer complete
DMA0REQ = 13; // Select ADC1 as DMA Request source
DMA0STA = __builtin_dmaoffset(BufferA);
DMA0STB = __builtin_dmaoffset(BufferB);
IFS0bits.DMA0IF = 0; //Clear the DMA interrupt flag bit
IEC0bits.DMA0IE = 1; //Set the DMA interrupt enable bit
DMA0CONbits.CHEN=1; // Enable DMA
}

37
 Locate buffer for DMA
#define MAX_CHNUM 13 // Highest Analog input number (AN4,AN5,AN10,AN13)
#define SAMP_BUFF_SIZE 8 //size of input buffer/channel
#define NUM_CHS2SCAN 4 //Number of channels
// Number of locations for ADC buffer = 14 x 8 = 112 words
//The buffer should be aligned to 128 words or 256 bytes
int BufferA[MAX_CHNUM+1][SAMP_BUFF_SIZE] __attribute__((space(dma),aligned(256)));
int BufferB[MAX_CHNUM+1][SAMP_BUFF_SIZE] __attribute__((space(dma),aligned(256)));

38
 Interrupt function
void __attribute__((interrupt, no_auto_psv)) _DMA0Interrupt(void)
{
if(DmaBuffer == 0)
{
// ProcessADCSamples(&BufferA[4][0]);
ProcessADCSamples(&BufferA[5][0]);
}
else
{
// ProcessADCSamples(&BufferB[4][0]);
ProcessADCSamples(&BufferB[5][0]);
}
DmaBuffer ^= 1;
IFS0bits.DMA0IF = 0; // Clear the DMA0 Interrupt Flag
}

39
 Singal processing function
void ProcessADCSamples(int * AdcBuffer)
{
int a=0;
int i=0;
while(i<8)
{
a+=*AdcBuffer++; //simple averaging
i++;
}
LATA=a>>5; //divison by 4 to show the ten bit value on 8 leds and divison by 8 due to
the averaging
}

04 adc (pic24, ds pic with dma)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to 04 adc (pic24, ds pic with dma)

Similar to 04 adc (pic24, ds pic with dma) (20)

04 adc (pic24, ds pic with dma)