problem in interfacing LTC2410 with 18LF2520

[hemnath]

Hardware Connections:
18LF2520 --------- LTC2410
PIN C4 ---------- SDO
PIN C3 --------- SCK
PIN C1 --------- CS

test code:

#include "18F2520.h"
#fuses INTRC, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP      // Internal oscillator
#use delay(clock=1000000)      // 1Mhz

#define A2D_CSI       PIN_C1     
#define A2D_SCLK      PIN_C3     
#define A2D_SDO      PIN_C4   

int32 Read_A2D(void)
{
   int32 A2D_COUNTS;
   int i;

   output_high(A2D_SCLK);
   delay_us(100);
   output_high(A2D_CSI);
   output_low(A2D_SCLK);
   output_low(A2D_CSI);

   while((input(A2D_SDO))==1); //wait for /EOC to go low...

   for(i=4;i>0;i--) //I don't need to use these first 4 bits
   {
      output_high(A2D_SCLK);
      delay_us(5);
      output_low(A2D_SCLK);
      delay_us(5);
   }

   for(i=20;i>0;i--)      //Set i = number of bits to read
   {                     
      output_high(A2D_SCLK);
      delay_us(5);
      shift_left(&A2D_COUNTS,4,input(A2D_SDO));
      output_low(A2D_SCLK);
      delay_us(5);
   }
   output_high(A2D_CSI);

   return A2D_COUNTS;
}

void main()
{
   int32 A2D_value;
   setup_adc_ports(NO_ANALOGS|VSS_VDD);         // No analogs
   setup_adc(ADC_OFF|ADC_TAD_MUL_0);
   
   setup_comparator (NC_NC_NC_NC);      // Disable comparator

   while(1)
   {
          A2D_value = Read_A2D();
          delay_ms(200);
          // display the adc value on lcd
    }
}

When i run this code, I get the output of 709931 in the display. When the change the input voltage at LTC2410, the display value is not changing.

Please help

 

[KlausST]

Hi,

why you use bit bang mode instead of built in SPI hardware?

Klasu

 

[hemnath]

sorry. There was a problem on the hardware. SCK and SDO lines are wrong connected.

I want to receive 32 bit data from LTC2410. I modified the routine. But it's not working.

int32 Read_A2D(void)
{
   int32 A2D_COUNTS;
   int i;

   output_high(A2D_SCLK);
   delay_us(100);
   output_high(A2D_CSI);
   output_low(A2D_SCLK);
   output_low(A2D_CSI);

   while((input(A2D_SDO))==1); //wait for /EOC to go low...
   for(i=32; i>0; i--)      //Set i = number of bits to read
	{                     
      output_high(A2D_SCLK);
      delay_us(5);
      shift_left(&A2D_COUNTS, 4, input(A2D_SDO));
      output_low(A2D_SCLK);
      delay_us(5);		
   }
   output_high(A2D_CSI);

   return A2D_COUNTS;
}

How to use SPI hardware?

Also LTC2410 has internal oscillator. Im using the internal serial clock.

 

[paulfjujo]

hello

where do you configure I/O
A2D_SDO must be configured as input for reading the bit value.

try this

int dummy;
   for(i=20;i>0;i--)      //Set i = number of bits to read
   {                     
      output_high(A2D_SCLK);
      delay_us(5);
     dummy=input(A2D_SDO);
      shift_left(A2D_COUNTS,4,dummy);        // A2D_COUNT insrtead of &A2D_COUNT
      output_low(A2D_SCLK);
      delay_us(5);
   }

 

[KlausST]

Hi,

sorry. There was a problem on the hardware. SCK and SDO lines are wrong connected.

your config seems to be with SCK and SDO like PIC datasheet.
Is it really a hardware problem?

Hardware Connections:
18LF2520 --------- LTC2410
PIN C4 ---------- SDO
PIN C3 --------- SCK
PIN C1 --------- CS

Klaus

 

[hemnath]

I wrongly connected in the hardware as
18LF2520 --------- LTC2410
PIN C3 ---------- SDO
PIN C4 --------- SCK
PIN C1 --------- CS

- - - Updated - - -

Hi paulfjujo,
I want to read 32 bit data. In the datasheet, it says LTC2410 produces 32 bit output code. Below is the code. But still there is an error.

int32 Read_A2D(void)
{
   int32 A2D_COUNTS;
   int i;

   output_high(A2D_SCLK);
   delay_us(100);
   output_high(A2D_CSI);
   output_low(A2D_SCLK);
   output_low(A2D_CSI);

   while((input(A2D_SDO))==1); //wait for /EOC to go low...
   for(i=32; i>0; i--)      //Set i = number of bits to read
	{                     
      output_high(A2D_SCLK);
      delay_us(5);
      shift_left(A2D_COUNTS, 4, input(A2D_SDO));
      output_low(A2D_SCLK);
      delay_us(5);		
   }
   output_high(A2D_CSI);

   return A2D_COUNTS;
}

Then i shall parse it to 24 bit data.

 

[hemnath]

I have designed a PCB and components are soldered and testing on it. (Not testing on breadboard).

Measured Vref: 3.2938V

Measured Input signal, Vin = IN+ - IN- => 0.00048V.

Maximum change in input signal is 4uV. For these change in input signal, there could be change of 20 bits.
1uV = 5 bits.

int32 Read_A2D(void)
{
   int i;
   signed int32 data = 0;

   output_high(A2D_SCLK);
   delay_us(100);
   output_high(A2D_CSI);
   output_low(A2D_SCLK);
   output_low(A2D_CSI);

   data = 0;

   for (i = 32; i!=0; i--)
   {
      output_high(A2D_SCLK); //clock hi
      delay_us(5);
      if (input(A2D_SDO))
      bit_set(Data, i - 1);
      output_low(A2D_SCLK); //clock low
      delay_us(5);
   }

   output_high(A2D_CSI);

   return data;
}

But the output code changes in values of 1000.. Please help me to correct the above routine.

 

[KlausST]

Hi,

How to use SPI hardware?

--> read PIC datasheet.


What about debugging?

Instead of looking only at the END values on the LCDisplay you should go step by step.

First measure VCC, FO, REF+, REF- IN+, IN- all with respect to ground.
Show us the values.

you have a 32 bit result from ADC,
* Bits 31...30 are status bits. What do they show?
* Bits 29 is the sign bit. What does it show?
* Bits 28..5 is the conversion result. What does it show? (unchanged. without any correction, just the raw bits)
* bits 4..0 don´t have a meaning.

for calculation you need bits 29 ... 5.
Use a "32 bit signed int" result value.
* put ADC bit 29 into result bit 31
* put ADC bits 28..5 into result bits 30.. 7
* put "0" in result bits 6...0
* invert result bit 31

the 32 bit signed result value range equals the ADC input range.

Klaus