Specifications

dsPIC33F Family Reference Manual

Example 16-4: Code for Channel Scanning Using DMA (Continued)

//AD1CHS123: A/D Input Select Register

AD1CHS123bits.CH123SA = 0; // MUXA +ve input selection (AIN0) for CH1

AD1CHS123bits.CH123NA = 0; // MUXA -ve input selection (Vref-) for CH1

//AD1CSSH/AD1CSSL: A/D Input Scan Selection Register

AD1CSSH = 0x0000;

AD1CSSL = 0x000F; // Scan AIN0, AIN1, AIN2, AIN3 inputs

AD1CON1bits.ADDMABM = 0; // DMA buffers are built in scatter/gather mode

AD1CON2bits.SMPI = 3; // 4 ADC buffers

AD1CON4bits.DMABL = 3; // Each buffer contains 8 words

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

}

/*======================================================================================

Timer 3 is setup to time-out every 125 microseconds (8Khz Rate). As a result, the module

will stop sampling and trigger a conversion on every Timer3 time-out, i.e., Ts=125us.

=======================================================================================*/

void initTmr3()

{

TMR3 = 0x0000;

PR3 = 4999; // Trigger ADC1 every 125usec

IFS0bits.T3IF = 0; // Clear Timer 3 interrupt

IEC0bits.T3IE = 0; // Disable Timer 3 interrupt

T3CONbits.TON = 1; //Start Timer 3

}

// Linker will allocate these buffers from the bottom of DMA RAM.

struct

{

unsigned int Adc1Ch0[8];

unsigned int Adc1Ch1[8];

unsigned int Adc1Ch2[8];

unsigned int Adc1Ch3[8];

} BufferA __attribute__((space(dma)));

struct

{

unsigned int Adc1Ch0[8];

unsigned int Adc1Ch1[8];

unsigned int Adc1Ch2[8];

unsigned int Adc1Ch3[8];

} BufferB __attribute__((space(dma)));;

// DMA0 configuration

// Direction: Read from peripheral address 0-x300 (ADC1BUF0) and write to DMA RAM

// AMODE: Peripheral Indirect Addressing Mode

// MODE: Continuous, Ping-Pong Mode

// IRQ: ADC Interrupt