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4922 SPI not working

 
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Sid2286



Joined: 12 Aug 2010
Posts: 119

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4922 SPI not working
PostPosted: Fri Nov 22, 2013 3:29 am     Reply with quote
Hi,

i tired the following code, but its not working...
not sure what is the problem.
Code:

void write_dac(int16 dac_value)
{
   char i;
   char temp;
   output_low(DAC_CS);
   output_high(DAC_LDAC);
   temp=(dac_value>>8) & 0xFF;
   temp=temp|0x30;
   
   for(i=0;i<8;i++)
   {
      output_high(DAC_CLK);
      output_bit(DAC_DI,((temp<<1)&0x80));
      output_low(DAC_CLK);
      delay_ms(100);
   }
   temp=dac_value;
   for(i=0;i<8;i++)
   {
      output_high(DAC_CLK);
      output_bit(DAC_DI,(temp<<1)&0x80);
      output_low(DAC_CLK);
      delay_ms(100);                                         
   }
   output_high(DAC_CS);
   output_low(DAC_LDAC);


thanks,
Sid
Ttelmah



Joined: 11 Mar 2010
Posts: 19505

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PostPosted: Fri Nov 22, 2013 4:35 am     Reply with quote
Why not use the SPI drivers supplied?..... Even if you must use software SPI (chip doesn't have the hardware), CCS has working code that is likely to be much more efficient than this.....

There are quite a few things wrong though:

a) LDAC, must be _high_ at the start before the CS drops. At the end of the sequence, CS needs to go high, then LDAC drop, and rise again. This is what transfers the data to the DAC.
b) You should also make sure you start with the clock low before CS drops.
c) You are rotating the byte, before you perform the 'and'. You will be sending bit 7 as the first bit.....
d) Data is clocked on the rising edge of CS, not the falling edge.
e) You don't need/want the delays.
f )You seem to be calling your data output pin 'DI'. Designed to confuse.

So:
Code:

void send_byte(int8 val)
{
   int8 mask=0x80; //clock out 8 bits starting from bit 7
   do
   {
       if (mask&val)
          output_high(DAC_DI);
       else
          output_low(DAC_DI);
       output_high(DAC_CLK);
       mask>>=1;
       output_low(DAC_CLK);
    }
    while (mask!=0);
}

void write_dac(int16 dac_value, int1 unit)
{
   output_high(DAC_LDAC);
   output_low(DAC_CLK); //ensure lines start at correct levels
   dac_val &=0x0FFF; //Twelve bits to send
   bit_set(dac_val,12); //shutdown off
   bit_set(dac_val,13); //low gain
   if (unit)
      bit_set(dac_val,15); //select channel
   output_low(DAC_CS);
   send_byte(make8(dac_val,1)); //send MSB
   send_byte(make8(dac_val,0)); //send LSB
   output_high(DAC_CS); //complete transfer
   //now clock the byte into the DAC registers
   output_low(DAC_LDAC);   
   output_high(DAC_LDAC);
}

Adds a 'unit' variable to select the channel to use.

Now the 'send_byte' code could be replaced with the standard spi_xfer command, and #use SPI on the same pins.

No guarantees, typed from the data sheet, and untested, but should give the signal required by the chip.

Best Wishes
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