ADS1256: ADS1256 and TM4C129 SSI communication issue

Hi,

Thanks for getting back to me. I made some changes and ran the code. It seems one of the issue is the sclk frequency used.  It seems I can read back the values of the registers

01h,03h and 04h. The registers 00h gives random values and 02h returns nothing on the miso line. I am attaching the code and also the spi communication on the oscilloscope.

#include <stdint.h>

#include <stdbool.h>

#include "inc/hw_memmap.h"

#include "inc/hw_ssi.h"

#include "inc/hw_types.h"

#include "driverlib/ssi.h"

#include "driverlib/gpio.h"

#include "driverlib/pin_map.h"

#include "driverlib/sysctl.h"

#include "UART.h"

#include "driverlib/uart.h"

uint32_t ui32SysClkFreq;

int i;

uint8_t k,j=0;

char buffer [sizeof(long)*8+1];

int main(void)

{

uint32_t ui32Index;

long ui32Data[4] =1;

ui32SysClkFreq = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ | SYSCTL_OSC_MAIN |

SYSCTL_USE_PLL | SYSCTL_CFG_VCO_480), 120000000);

/*Uart initialization*/

SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA); // Port A for Uart

GPIOPinConfigure(GPIO_PA0_U0RX);

GPIOPinConfigure(GPIO_PA1_U0TX);

GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

UARTConfigSetExpClk(UART0_BASE, ui32SysClkFreq, 9600,(UART_CONFIG_WLEN_8 |

UART_CONFIG_STOP_ONE | UART_CONFIG_PAR_NONE));

/*SPI initialization*/

SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI2);

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPION); // CS control

GPIOPinTypeGPIOOutput(GPIO_PORTN_BASE, GPIO_PIN_4);

GPIOPinTypeGPIOInput(GPIO_PORTN_BASE, GPIO_PIN_5); //DRDY

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);

GPIOPinConfigure(GPIO_PD3_SSI2CLK);

SSIAdvModeSet(SSI2_BASE,SSI_ADV_MODE_LEGACY);

GPIOPinConfigure(GPIO_PD1_SSI2XDAT0);

GPIOPinConfigure(GPIO_PD0_SSI2XDAT1);

GPIOPinTypeSSI(GPIO_PORTD_BASE,GPIO_PIN_3|GPIO_PIN_2|GPIO_PIN_1|GPIO_PIN_0);

SSIConfigSetExpClk(SSI2_BASE, ui32SysClkFreq, SSI_FRF_MOTO_MODE_1,

SSI_MODE_MASTER, 2000000, 16);

SSIEnable(SSI2_BASE);

GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_4,16);

GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_4,0); // deasserting CS

//send reset command

while(GPIOPinRead(GPIO_PORTN_BASE, GPIO_PIN_5)){}; // check DRDY line

for(i=0; i<1000;i++) // delay before first SCLK

SSIDataPut(SSI2_BASE, 0xfe); // reset command

while(SSIBusy(SSI2_BASE))

{

}

SSIDataPut(SSI2_BASE,0x0f);  // SDATAC command

while(SSIBusy(SSI2_BASE))

{

}

           //WREG DRATE COMMMAND

SSIDataPut(SSI2_BASE, 0x53);

for(i=0; i<1000;i++)

SSIDataPut(SSI2_BASE, 0x00);

for(i=0; i<1000;i++)

SSIDataPut(SSI2_BASE, 0xa1);

for(i=0; i<1000;i++)

while(SSIBusy(SSI2_BASE))

{

}

for(i=0; i<1000;i++);

       /*WREG MUX

SSIDataPut(SSI2_BASE, 0x51);

while(SSIBusy(SSI2_BASE))

{

}

SSIDataPut(SSI2_BASE, 0x00);

while(SSIBusy(SSI2_BASE))

{

}

SSIDataPut(SSI2_BASE, 0x01);

while(SSIBusy(SSI2_BASE))

{

}*/

while(1)

{

GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_4,0); // deasserting CS

/*read DRATE register*/

while(GPIOPinRead(GPIO_PORTN_BASE, GPIO_PIN_5)){}; // check DRDY line

SSIDataPut(SSI2_BASE, 0x11); // send 1st command byte -0b00010000

for(i=0; i<100;i++)

SSIDataPut(SSI2_BASE, 0x00); // send 2nd command byte -0b00000000

while(SSIBusy(SSI2_BASE))

{

}

// SSIDataGet(SSI2_BASE, &ui32Data[0]);

GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_4,16); // asserting CS

}}

Miso(Purple) - read back value(01h) =01h

(13h) read back value = F0h

similarly, I got E0h for (14h- register). I cannot also write to the registers it seems. 

Hi Mustahsin,

I have a couple of suggestions to try:

• I would recommend using 8-bit SPI frame (instead of 16-bit frames as you are currently using). The reset command is only 8-bits and not all other commands will be a multiple of 16 bits, so it may be easier to simply send SPI command byte by byte.
  
  
• The 2 MHz SCLK is a little fast for the ADS1256 if you're using the nominal 7.68 MHz ADC clock. The SPI clock should not exceed 1/4th the frequency of the ADC clock, so you might try using a a slightly lower SCLK frequency.
  
  
• The continuous SCLK is probably causing some issues with reading registers. The ADS1256 has a t6 delay required between the command bytes and the register data byte(s). See figure 34 in the ADS1256 datasheet.
  
  
• If you can try to capture a single RREG command on the oscilloscope with the /CS signal included so that you can see how this command is framed. For troubleshooting, it is okay to loop 1000 times, but I would recommend including the toggling of /CS in the loop to make it easier to differentiate between commands.