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FDC2214: Data acquisition control

YOSHIHIRO KANEKO
Prodigy 40 points
Part Number: FDC2214

Tool/software:

Hi, 

I'd like to confirm the periodical data acquisition sequence for 3ch sensing. I understand there are 3 ways. 

Method 1. INTB trigger

MCU gets the data ready flag via INTB by setting DRDY_2INT in ERROR_CONFIG(0x19) to b'1.

When INTB is asserted, MCU read DATA_CH0-2, DATA_LSB_CH0-2 via I2C

This requires INTB connection between FDC2214 and MCU.

Method 2. Watch DRDY register

MCU watch DRDY register in STATUS(0x18) periodically.

If DRDY is b'1, read DATA_CH0-2, DATA_LSB_CH0-2 via I2C.

This does not require INTB connection between FDC2214 and MCU.

Method 3.Polling DATA_CH0-2, DATA_LSB_CH0-2

MCU just periodically read DATA_CH0-2, DATA_LSB_CH0-2 via I2C.

This does not require INTB connection between FDC2214 and MCU.

---

a)Are these expected procedure ?

b)How should I handle CHx_UNREADCONV register in STATUS(0x18)  ? Is it mandatory to read here in periodical data acquisition ?

c)While FDC2214 data conversion is activated, are DATA_CH0-2, DATA_LSB_CH0-2 updated automatically with designed sampling rate ? Or keep the value until MCU read the DATA_CH0-2, DATA_LSB_CH0-2 ?

For example FDC2214's 3ch total sampling period is 5ms, that is 200Hz sampling. On the other hand, MCU polling period is 10ms. In this case, is half of data in FDC2214  skipped ?

   FDC 2214 : t1_data_3ch -> 5ms -> t2_data_3ch -> 5ms -> t3_data_3ch -> 5ms  -> t4_data_3ch -> 5ms  -> t5_data_3ch -> 5ms  ...

   MCU can capture t1_data_3ch, t3_data_3ch, t5_data_3ch ...

 

Regards,

Kaneko

  • 0
    TI__Mastermind 40400 points

    Hello Kaneko,

    a. Yes, these are the expected data aquisition methods.  

    b. The status register is cleared when you read the DATA_CHx register.  

    c. The data will be overwritten when a new conversion is completed.  Yes, if your total conversion time is half of the polling time, you will miss half of the measurements.  The total conversion time of the FDC2214 is deterministic based on your configuration, so you can use this to determine what your polling period should be.  This is described starting on page 16 of the datasheet.  

  • 0 in reply to Eddie LaCost
    Prodigy 40 points

    Hi, 

    Thank you for your explanation. In my system, number of GPIO is limited.

    So it was good that INTB connection is not mandatory.

    What is the expected usage of CHx_UNREADCONV register ?

    Could you show an usage example ?

    Regards,

    Yoshihiro

  • 0 in reply to YOSHIHIRO KANEKO
    TI__Mastermind 40400 points

    Yoshihiro,

    The CHx_UNREADCONV register could be checked to determine when a new conversion has occurred, but not read out yet.  In general, if you use the deterministic approach, this should not be necessary.