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PIC driving an external DAC?

 
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bwgames



Joined: 21 Jul 2005
Posts: 36

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PIC driving an external DAC?
PostPosted: Fri Aug 12, 2005 3:49 am     Reply with quote
Hiya,

I realise this isn't strictly PIC C related, but maybe you can shed some light.

I am using a PIC to control a DAC (MAX5712). To diagnose this problem, I've connected digital in (DIN) to the PIC (it would normally be connected to an opto-coupler), as well as SCLK and CS.

My code is as follows:

Code:


#define Fosc 40000000           
#include <18F8621.h>
#DEVICE *=16 ADC=8
#include <string.h>
#include <stdio.h>

//-------------------------------------------------------------------------------------
// DEFINES
#define LED PIN_C0
#define DLED PIN_C1
#define ADC_SCLK PIN_E0
#define ADC_CS PIN_E2
#define DAC_SCLK PIN_H6
#define DAC_CS PIN_H7      
#define DAC_PIC_CTRL PIN_H5
//-------------------------------------------------------------------------------------
// COMPILER DIRECTIVES and HARDWARE CONFIGURATION
#use delay(clock = Fosc)

#fuses EC_IO
#fuses NOOSCSEN      // Oscillator System Clock Switch Disabled
#fuses NODEBUG      // No Background Debugger
#fuses NOLVP         // Low Voltage ICSP Disabled
#fuses NOPROTECT    // No Code Protect
#fuses NOWDT         // No onboard watchdog
#fuses PUT            // Power Up Timer Enabled
#fuses BROWNOUT      // Brown Out Reset enabled

#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7,parity=N,bits=8)     

static short ADCFlag = 1;
static short DACFlag = 1;
static short DACCS = 1;
static short ADCCS = 1;

int trcnt = 0;
int trackk=0;
int8 MaxV[16]={0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1};

// MAIN
void main()
{
   while(true)
{
if(trcnt==0){output_bit(DAC_CS,1); };
if(trcnt==4){  DACFlag=1; ADCFlag=1; output_bit(DAC_CS,0); DACCS=0; output_bit(ADC_CS,0);  ADCCS=0; output_bit(DAC_SCLK,1);  };

      if((trcnt>=4)&&(trcnt<=37)){ output_bit(DAC_CS,0);  DACCS=0; if(DACFlag==0){output_bit(DAC_PIC_CTRL,MaxV[trackk]); trackk=++trackk;}; output_bit(DAC_SCLK,DACFlag);};

if(trcnt==38){output_bit(ADC_CS,1); ADCCS=1; output_bit(DAC_CS,1); DACCS=1;};
   
      ADCFlag=~ADCFlag;
      DACFlag=~DACFlag;
      trcnt=++trcnt;   
       delay_cycles(75); //set back to  50
      if(trcnt==45){trcnt=0; trackk=0;}; //set back to 30
};
}


Edit:

Bottom of my post appears to have been lopped off.
The DAC datasheet specifies 4 leading zeros, which it reads in on the falling edge of SCLK, followed by a 12bit DAC code, i.e. 12 1's for maximum output.
The oscilloscope output seems fine, 4 leading zero's on the falling edge of SCLK, followed by the 12 bits...

Is it something obvious I'm overlooking? Have tried different DACs, so I doubt the DAC is faulty....
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Fri Aug 12, 2005 6:13 am     Reply with quote
And your problems is?????????????
Ttelmah
Guest
PostPosted: Fri Aug 12, 2005 6:16 am     Reply with quote
I drove this chip some time ago.
The driver routine was:
Code:


void send_dac(int16 val) {
   int8 mask;
   int8 ctr;
   mask=0x8000;
   DAC_CS=0;
   for (ctr=0;ctr<32;) {
      if (ctr&1) {
          DAC_CLK=0;
      }
      else {
           DAC_CLK=1;
           if (val & mask) output_bit(DAC_DAT,1);
           else output_bit(DAC_DAT,0);
           mask /=2;
      }
      ctr++;
   }
   DAC_CLK=1;
   DAC_CS=1;
}


DAC_DAT, DAC_CS, and DAC_CLK were connected to and defined as the three control pins.

This was called with:
Code:

#define WAKE (0xF000)

   send_dac(WAKE);
   send_dac(val_to_send);


Your code looks bulkier than this (and requires sixteen numbers, instead of just a single 16bit value). However I'd suspect the 'key' difference is sending the 'WAKE' value first. If I remember correctly, the chip has the ability to go into a low power 'sleep' mode, and you must wake it up, before sending a value.

Best Wishes
Guest
PostPosted: Fri Aug 12, 2005 10:44 am     Reply with quote
WAKE was indeed the problem Embarassed

But that code looks much more flexible than mine, will take a look at it thanks Smile
bwgames



Joined: 21 Jul 2005
Posts: 36

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PostPosted: Tue Aug 16, 2005 4:23 am     Reply with quote
Been trying to get your code above working, and can't seem to get any data output, I get the CS and SCLK out fine, but nothing on the DATA, even for WAKE.

Only modifications I've made is to replace (e.g.) DAC_CS =1 with output_bit(DAC_CS,1) etc.

I'm assuming you are doing bit masking, hence the val & mask, but what does the mask /= 2; line do? Can't seem to find any reference to /= Question

thanks Very Happy
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Tue Aug 16, 2005 6:02 am     Reply with quote
Standard C

mask = mask / 2;
DragonPIC



Joined: 11 Nov 2003
Posts: 118

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PostPosted: Tue Aug 16, 2005 10:24 am     Reply with quote
Mark wrote:
Standard C

mask = mask / 2;


Same as:

mask >>= 1;

or

mask = mask >> 1;
_________________
-Matt
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