ads1256 data conversion

Dear Tom

Thanks for your quick answer, I'm attach oscilloscope waveform what you want

As I told, I want to read adc register using RREG command , but there is no answer(no DOUT)

Due to policy, It is impossible attach schematics.

AVDD : +5V

AGND, DGND ,D3, D2, D1,D0/CLKOUT : Connected GND

AINCOM , XTAL2 : NC

DVDD : 3V3

VREFP : +2.5V, VREFN: GND

XTAL1_CLKIN : External Clock 7.68Mhz from FPGA

AIN0,2,4,6 : ADC Input

AIN1,3,5,7 : +2.5V (For Full-Scale ADC)

RESET, /SYNC_PDWN : +3.3V

Dear Tom

I  saw /drdy pulse coming out the ads1256.

As I told, I couldn't read register which I wrote.

For example, If I wrote command 0X53 0x00 0x23,

I expect 0x23 when I read command, but there is no dout.

 CH2 is /SS(Slave Select).

I will modify /ss to maintain low through the entire communication process

Regards

Dear Tom

I modified /ss to maintain low through the entire communication process, but there is no dout also

Is there anything else to check for the communication??

regards

Jongho,

The SCLK should dwell low.  According to your scope shots it is dwelling high.  Also, there needs to be a small delay between the command and the data.  Review Figure 1 on page 6 of the data sheet for the required timing delay and communication requirements.

Best regards,

Bob B

Dear TI employee

Thanks to your helps, I could get digital data after analog to digital conversion.

But digital results make me disappointed.

There is 1mV difference between dmm(Digital multi-meter) and ADS1256 digital regults.

It looks like calibration(Self-gain, Self-offset) function is not working.

would you check my calibration process?

my pseudo codes are below.

==========================================

//read status register

 WriteBuffer[0] = 0x10;  WriteBuffer[1] = 0x00;

XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 2); //byte 2 byte

//make ads auto cal, buffer enable

 temp = ReadBuffer[0];  temp |= 0x6;

//write status register

WriteBuffer[0] = 0x50;  WriteBuffer[1] = 0x00;  WriteBuffer[2] = temp;

 ADS1256_WaitDrdy();  XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 3); //Send 3 byte

//write adcon register

WriteBuffer[0] = 0x52;  WriteBuffer[1] = 0x00;  WriteBuffer[2] = 0x01; //0x21

XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 3); //send 3byte

ADS1256_WaitDrdy();

//write drate register

WriteBuffer[0] = 0x53;  WriteBuffer[1] = 0x00;  WriteBuffer[2] = 0x13;

XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 3); //send 3 byte

ADS1256_WaitDrdy();

//wirte I/o register

WriteBuffer[0] = 0x54;  WriteBuffer[1] = 0x00;  WriteBuffer[2] = 0xE0;

XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 3); //send 3 byte

//write mux register

WriteBuffer[0] = 0x51;  WriteBuffer[1] = 0x00;  WriteBuffer[2] = 0x01;

XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 3); //byte 3 byte

//Self Cal again !!!!

WriteBuffer[0] = 0xF0;

XSpi_Transfer(&SpiADC, WriteBuffer, ReadBuffer, 1); //byte cnt

Wait(1000); //wait 1sec 

Best Regards

Jongho,

Can you send us your schematic/layout?  PCB layout if done poorly can have a negative impact on your results.  Also, calibration can be negatively impacted if you have a noisy reference.

Best regards,

Bob B

Dear Bob

Thanks to your opinion, but  it is impossible to send schematic/layout to you  because of company policy.

I have checked layout with my co-worker, but there is no problems.

My schematics are below.

1. reference 2.5V : ref5025a

2. AVDD : 5V, DVDD :3.3V

3. VREFP : 2.5V(reference), VREFN : DGND

3. AIN1,3,5,7 : 2.5V(reference), AIN0,2,4,6 : input, AINCOM : NC

4. D3,2,1,D0: DGND

5. /RESET, /SYNC_PDWN : 2.5V

6. XTAL2 : NC, XTAL1_CLKIN : external 7.68Mhz

8. /CS : GND

best regards

Jongho,

It is very difficult to guess what might be happening, and to know whether your DMM is accurate and calibrated.  The REF5025 will oscillate if there is not a large value cap at the output of the reference.  PCB layout is very critical in getting high levels of performance.

Best regards,

Bob B