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Driver for LTC2420 Delta Sigma ADC

 
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cbarberis



Joined: 01 Oct 2003
Posts: 132
Location: Punta Gorda, Florida USA

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Driver for LTC2420 Delta Sigma ADC
PostPosted: Mon Jul 06, 2009 6:17 pm     Reply with quote

Code:
/*********************************************************
*
*  LTC2420.c
*  Driver for LTC2420, SPI 20 bit Delta-Sigma  A/D converter
*  Compiled for CCS compiler V4 and up
*
*  C. Barberis
*  Bartek Technologies
*
*  Includes: None
*
**********************************************************
*
*
**********************************************************
**********************************************************
* Notes:
* Make sure to drive pin #8 with logic level from cpu, this pin controls internal filter
* for line rejection; Vcc = 50Hz and 0V = 60Hz
* Declare the appropiate I/O pin declarations for: FiltSel,ADCSEL,SDI,SDO and SCK before compiling this file
* Make sure to call (once) ExtAdcInit(); prior to reading adc values.
*********************************************************/

 //Function prototypes
 void ExtAdcInit(void);
 unsigned int32 ReadAdcValue(void);

 static short int AdcUnderFlow ;
 static short int AdcOverFlow;

  union { unsigned int32 AdcCode;
          struct {unsigned int8 AdcByte0;
          unsigned int8 AdcByte1;
          unsigned int8 AdcByte2;
          unsigned int8 AdcByte3;}AdcBytes; }AdcValue;

/////////////////////////////////////////////////////////////////////////////////

void ExtAdcInit() // Initialize LTC2420
{
   setup_spi(TRUE);
   setup_spi(SPI_MASTER|SPI_MODE_0_0|SPI_CLK_DIV_16|SPI_SS_DISABLED);   // change spi to low to high sense
   output_high(ADCSEL);
   FiltSel = 0;  // set for 60Hz filtering
   //FiltSel = 1; // set for 50Hz filtering
}

/////////////////////////////////////////////////////////////////////////////////

 unsigned int32 ReadAdcValue()     // Read LTC2420, SPI 20 bit Delta-Sigma ADC
  {
       AdcValue.AdcBytes.AdcByte3 = 0;             // highest byte of the 32 bit int is set to 0
       AdcUnderFlow = FALSE;
       AdcOverFlow = FALSE;
       output_low(ADCSEL);                          // bring ADCSEL line low to start conversion
       while(input(SDI))                            // Test for SDI low ready to start conversion
       restart_wdt();
       delay_us(500);                                // Start conversions after 500 uS delay
       AdcValue.AdcBytes.AdcByte2 = spi_read(0);     // read MSB, bits 23 to 16
       delay_us(10);                         // wait 10 uS before next byte read
       AdcValue.AdcBytes.AdcByte1 = spi_read(0);     // read bits 15 to 8
       delay_us(10);                         // wait 10 uS before next byte read
       AdcValue.AdcBytes.AdcByte0 = spi_read(0);     // read bits 7 to 0
       delay_us(10);                         // wait 10 uS before we raise ADCSEL chip enable
       output_high(ADCSEL);                          // bring ADCSEL line high to after end of conversion
       if( !bit_test(AdcValue.AdcBytes.AdcByte2,5))  // check to see if sign bit shows negative conversion
          AdcUnderFlow = TRUE;                       // if so send underflow error
       if( bit_test(AdcValue.AdcBytes.AdcByte2,4))   // check to see if extended range bit shows overflow condition
          AdcOverFlow = TRUE;                        // if so send overflow error
       if( bit_test(AdcValue.AdcBytes.AdcByte2,5) && !bit_test (AdcValue.AdcBytes.AdcByte2,4) )  // if everything is ok the mask data
             AdcValue.AdcBytes.AdcByte2&=0x0F;

       if(AdcUnderFlow) AdcValue = 0;                // if we detect an underrange contion return a zero value

       return(AdcValue.AdcCode);
                                          }


/////////////////// End of File /////////////////////////////////////////
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