AD5231 with ATmega32

[north2012]

Hi all,

I am using AD5231 with ATmega32 but I have problem to set wiper. Here is my code. Does anyone can see where is error because the resistance does not change whatever I send as command for wiper. I checked all hardware connections and everything seems to be good.

//#include<built_in.h>

sbit CLK at PORTB7_bit;
sbit CLK_Direction at DDB7_bit;

sbit DAT at PORTB5_bit;
sbit DAT_Direction at DDB5_bit;

sbit CS at PORTA4_bit;
sbit CS_Direction at DDA4_bit;

void set_pot(void)
{
   unsigned char i = 0;
   unsigned char cmd[3];
   unsigned long send = 0xb00300;

   CLK = 1; CLK = 1;
   CS = 0; CS = 0;
   for(i=0; i<24; i++)
   {
    if(send & 0x800000)
    {
    DAT = 1;
    }
    else
    {
    DAT = 0;
    }
    CLK = 0; CLK = 0;
    send = send << 1;
    CLK=1; CLK=1;
    } 
CS = 1; CS = 1;
}

void main()
{
  DAT_Direction = 1;     // define as output
  CLK_Direction = 1;     // define  as output
  CS_Direction = 1;     // define as output
  delay_ms(50);
  set_pot();
  while(1)
  {
  }
}

Thanks in advance.

 

[jayanth.devarayanadurga]

Why are you making clock and CS 0 two times and 1 two times.

CLK = 0
nop
CLK = 1

CS = 0
nop
CLK = 1

 

[north2012]

I am making it two times just to ensure enough time for stabilization. My hardware connections are:
Vcc-#WP, #PR and Vdd
GND - Gnd, Vss, T, B
SDI- DAT
CLK - SCK
#CS - #CS

 

[jayanth.devarayanadurga]

Post your circuit. Are you using RDY pin?

Try this code.

---

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//Pullup CS and CLK lines using 10k resistor
 
void Digital_POT_Write(unsigned int address, unsigned int data);
 
void main(){
 
    CLK = 1;
    CS = 1;
    
    for(i = 0; i < 1023; i++){
 
            Digital_POT_Write(0, i);
        _delay_ms(10);
 
    }
 
    while(1);
 
}
 
 
void Digital_POT_Write(unsigned int address, unsigned int data){
 
    unsigned char Command = 0xB0;
    unsigned char i = 0, byte1, byte0;
    
 
    CS = 0;
    Command = Command + address;
    byte1 = data >> 8;
    byte0 = data & 0xFF;
 
    for(i = 0; i < 8; i++){
        if(Command & 0x80)
            DAT = 1;
        else DAT = 0;
 
        CLK = 0;
        CLK = 1;
        Command = Command << 1;
    }
 
    for(i = 0; i < 8; i++){
        if(byte1 & 0x80)
            DAT = 1;
        else DAT = 0;
 
        CLK = 0;
        CLK = 1;
        byte1 = byte1 << 1;
    }
 
    for(i = 0; i < 8; i++){
        if(byte0 & 0x80)
            DAT = 1;
        else DAT = 0;
 
        CLK = 0;
        CLK = 1;
        byte0 = byte0 << 1;
    }
 
    CS = 1;
    CLK = 1;
 
}

---

 

[north2012]

I found bug in my code and here is working version written using microC for AVR compiler.

#include<built_in.h>
sbit CLK at PORTA1_bit;
sbit CLK_Direction at DDA1_bit;

sbit DAT at PORTA2_bit;
sbit DAT_Direction at DDA2_bit;

sbit CS at PORTA0_bit;
sbit CS_Direction at DDA0_bit;

void set_pot(unsigned int position)
{
   unsigned char i = 0;
   unsigned long send = 0xb00300;
   unsigned char set[3] = {0x00, 0x00, 0x00};
   set[0] = 0xB0;  //komanda za RDAC
   set[1] = Hi(position);
   set[2] = Lo(position);

   //send = 0x00b003ff;
   send = set[2]+256*set[1]+65536*set[0];
   
   CLK = 0;
   asm nop;
   CS = 0; 
   asm nop;
   for(i=0; i<24; i++)
   {
    if(send & 0x800000)
    {
    DAT = 1;
    asm nop;
    }
    else
    {
    DAT = 0;
    asm nop;
    }
    CLK = 1;
    asm nop;
    send = send << 1;
    CLK=0;
    asm nop;
    } 
CS = 1; 
asm nop;
}

void main()
{
  DAT_Direction = 1;     // define as output
  CLK_Direction = 1;     // define  as output
  CS_Direction = 1;     // define as output
  delay_ms(500);

  while(1)
  {
  set_pot(0x0100);
  delay_ms(3000);
  set_pot(0x03ff);
  delay_ms(3000);
  }
}

Now, I have another problem;

I read that tolerance is -40 to +20 % but I expected that resistance is linear in full range and for 0xb003ff I expected full scale resistance which should be around 39-40 kOhms. I measured Rwa resistance and for all measurements except last one the sum is equal to 39-40 Kohms.
Command Rwb Rwa
0xb00000 62.2 Ohms 39.74 kOhms
0xb00100 9.98 kOhms 29.78 kOhms
0xb00200 19.75 kOhms 19.86 kOhms
0xb00300 28.38 kOhms 9.94 kOhms
0xb003ff 33.29 kOhms 66.6 Ohms ????

Did anyone have similar experience?

Best regards.

 

[jayanth.devarayanadurga]

How are you getting 39-40 kOhms? The DPOT comes in 10K, 50k, or 100k. Are you using DPOTs in parallel?

 

[north2012]

I am using 50 kOhms version but I think that due the tolerance ( +20, -40%) it can be different from nominal value.

**broken link removed**