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AD7715 CCS driver annoying problem

 
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ac34856



Joined: 14 Dec 2009
Posts: 33
Location: Wales

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AD7715 CCS driver annoying problem
PostPosted: Mon Jan 25, 2010 9:58 am     Reply with quote

I've been testing the AD7715 which is the last thing I need to complete
a piece of code. This uses the driver supplied by CCS but so far I can
only get the program to output 0x00ff from the ADC.

If anyone has any ideas it would be much appreciated ... so I can get
this finished. Other bits work fine.

All of the signals appear to be correct and present - and the reference
voltage is 2.5V with a pot providing 0 to 2V input. The MCLK input is
1MHz.

As data is read out I am assuming it may be something to do with
the commands to setup the device. I put in a #define CLK_DEL to stretch out the clock and other SPI signals so this can be ignored as its set to
zero.

Compiler is 4.088

Code:

//*********************************************************//
//  Skeleton program for reading AD7715 using S/W SPI      //
//*********************************************************//
#include    <18F4620.h>

#device     PASS_STRINGS=IN_RAM
#fuses    HS, NOWDT, NOPROTECT, NOBROWNOUT, NOPUT, NOLVP
#use    DELAY(CLOCK=20000000) // , OSC=10000000)
#use      RS232(BAUD=115200, PARITY=N, XMIT=PIN_C0, BITS=8, ERRORS, RESTART_WDT, STREAM=COM1)
//#use       SPI(MASTER, DO=PIN_C5, DI=PIN_C4, CLK=PIN_C3,
// MSB_FIRST, MODE=0, BITS=16, STREAM=SPI_0)

#define    LED         PIN_D0
#define    ADC_CS       PIN_B0
#define    ADC_RESET    PIN_B1
#define    ADC_DRDY     PIN_B2
#define    ADC_CLK      PIN_B3
#define    ADC_DI       PIN_B4
#define    ADC_DO       PIN_B5
#define      CLK_DEL      0      // Number of delay cycles of clock

void      adc_init(void);
void       write_adc_byte(BYTE);
int16       read_adc_value(void);
int16       read_adc_word(void) ;

int          main(void)
{
int16      data  =   0;
int16      adval = 0;
int16      count;

fprintf(COM1, "\r\n ** PROGRAM STARTING ** ");
adc_init();
fprintf(COM1, "\r\n ADC Reset (SPI Running !)");
// write_adc_byte(0x3a);      // This is normally to access data

while(1)
     {      output_toggle(LED);
         adval = read_adc_value();
         fprintf(COM1, "\r\n %Ld - Version 1.11 ADC Test : %04x", count++, adval);
     }


void   adc_init(void)
{      
      output_low(ADC_RESET);
      delay_ms(500);
         output_high(ADC_CLK);
         output_high(ADC_CS);         
                // Set low to AD7715 chip select low pin
         output_high(ADC_RESET);      
      // Set high to AD7715 reset low pin
         delay_ms(3000);
         write_adc_byte( 0x12 );     // Communications Register
         write_adc_byte( 0x62 );      // Setup Register info here
}

void    write_adc_byte(BYTE data) {
         BYTE i;

         output_low(ADC_CS);
         delay_us(20);
         for(i=1;i<=8;++i)
         {   output_low(ADC_CLK);
            delay_us(CLK_DEL);
               output_bit(ADC_DI, shift_left(&data,1,0));
               output_high(ADC_CLK);
            delay_us(CLK_DEL);
            }   output_high(ADC_CS);
}

int16    read_adc_word(void)
      {
         BYTE    i;
         long    data;

         output_low(ADC_CS);
      delay_us(CLK_DEL);
         for(i=1;i<=16;++i)
         {   
         output_low(ADC_CLK);
         delay_us(CLK_DEL);
               output_high(ADC_CLK);
         delay_us(CLK_DEL);
               shift_left(&data, 2, input(ADC_DO));
         delay_us(CLK_DEL);
            }   
      delay_us(CLK_DEL);
      output_high(ADC_CS);
         return(data);
}

int16    read_adc_value()
      {
               int16   value;

         while ( input(ADC_DRDY)  );
         while ( !input(ADC_DRDY) );
      while (  input(ADC_DRDY)  );

         write_adc_byte(0x3a);
         value = read_adc_word();
         return(value);
}
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Jan 25, 2010 11:26 am     Reply with quote

Quote:
int16 adval = 0;

fprintf(COM1, "\r\n %Ld - Version 1.11 ADC Test : %04x", count++, adval);

To display an 'int16', you need to use "%lx" in the format string.
(That's a lower case L).
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Mon Jan 25, 2010 12:03 pm     Reply with quote

Seems like you're setting a gain of 32 (in communication register) and MCLK of 2.45 MHz (in setup register).
ac34856



Joined: 14 Dec 2009
Posts: 33
Location: Wales

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PostPosted: Tue Jan 26, 2010 3:45 am     Reply with quote

Thanks for both comments. It turned out to be something more fundamental and as usual human error - the IC I bought was a 3.3V version, so now I've got the right one its fixed.

As ever always read the small print -
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