ADS8332: problem with ads8332 resolution reading

anthony g

Prodigy 50 points

Part Number: ADS8332
Other Parts Discussed in Thread: REF6050, REF02

Hi,

I try to use an ADC ADS8332 with SPI communication.

It seems to be work great.

I am able to configure the CFR register (the config is 0b011111111111);.

I tried also to read data value with manual trigger. But I have a problem with this part. I read well a 16 bits data but I have no noise on the data. And there is step on the data like the curve I join

I tried to insert some delay to slow down the acquisition process. But i have always the same results.

I have also the problem in automatic trigger.

Moreover sometimes, the EOC doesn't go to low when I put CONVST at low. So, I have to put back CONVST at high and low.

This is the code which I use to read channel 1 for example

uint16_t adc_read_channel_1()
{

    long t = millis;
    while(millis - t <5);
    
    CONVST_Clear();
    
    while(EOC_INT_CDI_Get()!=0)
    {
        CONVST_Set();
        CONVST_Clear();
    }
    
    while(EOC_INT_CDI_Get()==0);
    CONVST_Set();
    
    
    
    uint8_t send[4] =  {READ_DATA,0,};
    uint8_t receive[3] = {0};
    CS_ADC_Clear();
    SPI1_WriteRead(send, 2, receive, 3);
    CS_ADC_Set();
    
    if(receive[2] ==32)
        SYS_CONSOLE_PRINT("%i \n\r",((uint16_t)(receive[0]<<8) + receive[1]));
    
    
    return ((uint16_t)(receive[0]<<8) + receive[1]);
}

And the schematic

Thank you for your help and sorry for my bad english!

Best regards,

Anthony

over 5 years ago

0 Keith Nicholas over 5 years ago

TI__Mastermind 48040 points

Hello Anthony,

It appears that you have a timing issue in your communications. If you could capture the waveforms using a logic analyzer or an oscilloscope, that would be helpful.

If I am reading your code correctly, it appears you have /CONVST inverted. /CONVST should be held high, and when you are ready to start a conversion, set it low and then high again. Wait for EOC to return high, and then read your data. Also, you are trying to read data while converting (EOC LOW), which requires that you read your data before the end of conversion. Since I cannot tell what frequency you are using, I suggest you READ WHILE SAMPLING, per Figure 1 in the datasheet.

Please adjust your code as follows:

1. Set /CONVST low, and then return high to start the conversion.
2. Delay ~1uS
3. Monitor EOC and wait for it to return HIGH
4. Once EOC returns high, take /CS low and clock the conversion result (16SCLK with SDI 0x1101000000000000b)
5. Return /CS HIGH
6. Repeat Step 1

Also, the REF02 output cannot directly drive the ADC inputs and get anywhere near the noise performance of the ADC. You should either add a reference buffer, per Figure 51 in the datasheet, or use the REF6050, which includes a high speed buffer suitable for driving the REF input of the ADS8332.

Regards,
Keith Nicholas
Precision ADC Applications

0 anthony g over 5 years ago in reply to Keith Nicholas

Prodigy 50 points

Hello,

thank you for your help.

I change the code like this.

    long t = 0;
    CONVST_Clear();  
    CONVST_Set();
    
    
    
    t = micros;
    while(micros - t <10);  //wait 10us
    
    while(EOC_INT_CDI_Get()!=1)SYS_CONSOLE_PRINT("WAIT");
    
    uint8_t send[2] =  {0xD0,0x00};
    uint8_t receive[3] = {0};
    CS_ADC_Clear();
    SPI1_WriteRead(send, 2, receive, 3);
    CS_ADC_Set();
    
    if(receive[2] ==32)
        SYS_CONSOLE_PRINT("%i      %i    %i %i\n\r",((uint16_t)(receive[0]<<8) + receive[1]),receive[0],receive[1],receive[2]);

And I have same results

And there is the tab of data (value of adc(MSB+LSB), MSB , LSB, TAG)

We have only three possible value on LSB.... I don't know why.

3107	12	35	32
3139	12	67	32
3331	13	3	32
3331	13	3	32
3587	14	3	32
3843	15	3	32
4099	16	3	32
4227	16	131	32
4355	17	3	32
4611	18	3	32
5187	20	67	32
5187	20	67	32
5251	20	131	32
5251	20	131	32
5379	21	3	32
5635	22	3	32
5763	22	131	32
6147	24	3	32
6275	24	131	32
6403	25	3	32
7235	28	67	32
7235	28	67	32
7235	28	67	32
7299	28	131	32
7299	28	131	32
7427	29	3	32
7427	29	3	32
7683	30	3	32
7939	31	3	32
8195	32	3	32
8195	32	3	32
9283	36	67	32
9283	36	67	32

I will try to make a capture of signals with logic analyzer.

Anthony

0 anthony g over 5 years ago in reply to anthony g

Prodigy 50 points

I make a capture with a digital analyzer.

And I read with my microcontroller

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

19523 76 67 32

It seems to be correct?

0 Keith Nicholas over 5 years ago in reply to anthony g

TI__Mastermind 48040 points

Hello Anthony,

The timing between EOC, /CS, and SCLK all look correct. However, I cannot tell if the timing requirements are met for SDI relative to SCLK edge.

Can you provide a zoomed in version of the above data showing the first 16 SCLK's and the SDI line?

Also, what is the frequency of SCLK?

Regards,
Keith

Data converters

Data converters forum

ADS8332: problem with ads8332 resolution reading