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PGA970: ADC and demodulator testing

Piyusha
Prodigy 110 points
Part Number: PGA970

Hi,

I am currently working on a project in order to build a new LVDT system using PGA970, achieving 14-bit resolution within a travel range of 2mm. I am testing the working of the PGA970 ADC and the demodulator. I am using SPI protocol to communicate between PGA970 and the MCU and output the LVDT position via the UART (RS232). As the secondary signal is very weak I am constructing an external amplifier in order to amplify it.

The datasheet (pg 42) states that “read data is available on the next SPI transfer. That is, when reading from a memory location, the user must send a subsequent transfer to get the data back. Further, the SPI response contains 16 bits of data. The logic returns data from a 16-bit aligned address; that is SPI reads should not straddle a 16-bit address boundary.”

However, the demodulator register is 32 bits (of which 24bits have the data output). As each SPI read is 16 bits, please advise if it will take 2 cycles to read the demodulator data register. Will the data get distorted between the 2 cycles and is there any solution in order to me to retain the whole 32 bits of data.

Thanks,

Piyusha

  • 0
    TI__Mastermind 31655 points
    Hello Piyusha,

    You are correct that the demodulator register will likely update between two different read cycles with the digital interface. The PGA970 was designed to make use of the integrated cortex M0 processor. While the processor is running it can quickly read the data from the demod registers and save them to a temporary location before the value updates. However, while the processor is running, the digital interfaces do not have access to the data registers.

    The only way to get a reliable digital output from the demodulators is to use the communication buffer in firmware. The communication buffer, or COMBUF, is described in the datasheet. You can find detailed information on developing firmware for the PGA970 in the software user's guide here: www.ti.com/.../sldu024.pdf

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 110 points
    Hello Scott,

    Thank you for your reply. I will take look at the software user's guide.

    Regards,
    Piyusha