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AFE11612-SEP: Consecutive ADC read fails

atma kanojia
Prodigy 40 points
Part Number: AFE11612-SEP
Other Parts Discussed in Thread: MSP430FR5969

Tool/software:

Hi,

I am using MSP430FR5969 to set DACs and read ADCs from v62/22614-01xe (AFE11612PAPSEP). The AFE11612 is controlled over SPI bus (2 MHz clock) as a standalone device. When I read the ADCs consecutively I get zeros but if I put a delay at the end of each 3 byte SPI transaction I get data. The following is my setup for the AFE:

/* AFE configuration commands */
/*ADC internal ref, CMODE manual */
const uint8_t AFE_AMC_0[] = {0x4C, 0x34, 0x00};
/*False alarm protection bits */
const uint8_t AFE_AMC_1[] = {0x4D, 0x03, 0x70};
/*DAC config - Channels asynchronous out */
const uint8_t AFE_CONF_REG[] = {0x58, 0x00, 0x00}; // update DAC immediately

/* Enable ADC channels 0 - 6, 8-9 and 12 */
const uint8_t AFE_ADC_EN[] = {0x50, 0x6D, 0xD9};
const uint8_t AFE_PWR_DN[] = {0x6B, 0x7F, 0x90};

The delay, I arbitrarily chose, was 62.5 usec (using the __delay_cycles(1000) function and the MSP is running at 16 MHz). I read through the datasheet to see if there was some literature on timing but did not find anything that pointed to this issue.  Maybe there is an issue with my setup or the afe requires a delta T between reads. Can you please help ?

Thanks

Atma

  • 0
    TI__Genius 10670 points

    Hi Atma,

    It looks like you have the ADC in direct mode. When reading the ADC data, do you give the ADC time to convert all of the data? You'll need some amount of delay before you read the ADC registers. Another question, do you see any issue with the DACs or other write commands if you don't include a delay?

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 40 points

    Hi Erin,

    A few things:

    * The CMODE bit is set so the AFE is configured in auto mode (const uint8_t AFE_AMC_0[] = {0x4C, 0x34, 0x00};)

    Are you suggesting that I switch to direct mode?

    * for the DAC commands the value does not update if I run the code continuous loop, although reading back the dac register shows the correct written value. If I step through it then the DAC updates its output. Finally after writing to the dac if I  update the power down register the values update.

    * Since I am writing software for space application I cannot arbitrarily choose a delay and hope for the best. Is there a way to get specific time delay numbers from TI?

    Thanks

    Atma 

  • 0 in reply to atma kanojia
    TI__Genius 10670 points

    Hi Atma,

    Ah, yes the code does say you're in auto mode, my apologies! 

    It does sound like there's a required delay. According to the datasheet, CS has a required high time of 30ns (page 13). Can you confirm if the consecutive writes/reads are meeting this requirement?

    Thanks,
    Erin