Interfacing the ADS1255 to the MSP430F5438

Hello!



I want to connect the ADS1255 to the MSP430F5438 via SPI. After the initialisation of the MSP I want to write to the registers of the ADS. Afterwards I want to read them again to check if the right values are stored.

I can see that the right commands and values were transmitted to the ADC using a logicanalyzer.  But when I want to read the registers, the ADC just gives me back a lot of 0x00s or other random numbers but never the values I sent.

SCLK of the SPI is 2.9MHz, four - wire. The inactive state of the clock is low, data is changed on the first UCLK edge (rising) and captured on the following edge (falling).

Here is the code that i use to init the ADC:



P4OUT &= ~0x04;                                    //CS low
UCB3TXBUF = 0x0F;                                //send command to stop sending data continously
while((UCB3STAT & UCBUSY));            //wait until byte is sent
P4OUT |= 0x04;                                    //CS high
    
 __delay_cycles(100);
    
  while(P1IN & 0x04);                            //wait for DREADY of the ADC to get low
  P4OUT &= ~0x04;                                    //CS low
  UCB3TXBUF = 0xFE;                                //RESET
  while((UCB3STAT & UCBUSY));            //wait until byte is sent
  P4OUT |= 0x04;                                    //CS high
        
        __delay_cycles(100);
        
        
        P4OUT &= ~0x04;                                    //CS low
      UCB3TXBUF = 0x52;                                //write command + address of the register - write to 0x02 ADCON-register
       while((UCB3STAT & UCBUSY));            //wait until byte is sent
      UCB3TXBUF = 0x02;                                //(number of registers that will be written) -1
      while((UCB3STAT & UCBUSY));            //wait until byte is sent
      UCB3TXBUF = 0x00;                                //clock out on clk-pin of the ADC is OFF, PGA = 1,
       while((UCB3STAT & UCBUSY));            //wait until byte is sent
      UCB3TXBUF = 0xB0;                                //Samplerate = 2000 SPS
       while((UCB3STAT & UCBUSY));            //wait until byte is sent
        UCB3TXBUF = 0x00;                                //GPIO
       while((UCB3STAT & UCBUSY));            //wait until byte is sent
        P4OUT |= 0x04;                                    //CS high
    
        __delay_cycles(100);
        
        P4OUT &= ~0x04;                                    //CS low
      UCB3TXBUF = 0xFC;                                //send sync-command
       while((UCB3STAT & UCBUSY));            //wait until byte is sent
      UCB3TXBUF = 0x00;                                //send wake-up command
      while((UCB3STAT & UCBUSY));            //wait until byte is sent
        P4OUT |= 0x04;                                    //CS high
        
        __delay_cycles(100);
        
        P4OUT &= ~0x04;                                    //CS low
      UCB3TXBUF = 0xF0;                                //send command to stop send data continously
       while((UCB3STAT & UCBUSY));            //wait until byte is sent
      P4OUT |= 0x04;                                    //CS high
        while((!P1IN & 0x04));                    //wait for DREADY to go low -> calibration completed
        



Afterwards I read the register continously:

P4OUT &= ~0x04;                                                               //CS low for adc
  UCB3TXBUF = 0x11;                                                       //read command + address of the register
  while((UCB3STAT & UCBUSY));                                      //wait until byte is sent
    UCB3TXBUF = 0x02;                                                       //send number of registers to be read -1 
    while((UCB3STAT & UCBUSY));                                 //wait until byte is received
    __delay_cycles(120);                                                //wait until command is processed
    UCB3TXBUF = DUMMY;                                                  //read content of register
    while((UCB3STAT & UCBUSY));
        UCB3TXBUF = DUMMY;                                                 //read content of register
    while((UCB3STAT & UCBUSY));
    UCB3TXBUF = DUMMY;                                                   //read content of register
    while((UCB3STAT & UCBUSY));
  P4OUT |= 0x04;                                                                     //CS adc high
    __delay_cycles(1000000);


Where is the mistake that I do? Thank you all!