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SPI ADC Interface with Hercules TMS570LC4357 MibSPI

Mustafa Su
Prodigy 20 points

Other Parts Discussed in Thread: TMS570LC4357

Hi,

I want to make a SAR ADC interface with Hercules TMS570LC4357.

My ADC is 16 bit SAR ADC which has a serial SPI interface for data. (Linear Tech. LTC2323-16)

I want to connect this ADC to Hercules MibSPI port. At first it seems easy but when i go in detailed i am not sure if i can connect and get the data correctly.

ADC must be slave because SPICLK must be input to ADC so my MibSPI port must be master.

ADC has a CNV input to start conversion but this input must not have much jitter because of the SNR issues so i will use an external oscillator for this signal.

This CNV signal will be 1 MHz in as my sampling rate will be 1 MSPS.

At this point i decided to connect this CNV signal to one of GIO pin of MCU that will be input pin.

Then i will configure this input GIO pin as an event trigger for MibSPI to start TX.

When MibSPI starts to make transmission the SPICLK will be output so the ADC will give the data.

On the orherside i will configure the DMA in order to transfer the mibSPI RX data to the Memory.

I am thinking that by using this way i can get 16384 samples of ADC data without interrupting my software.

Is this the true way to make a SAR ADC interface by Hercules MCU.

Any other design ideas ?

Thanks.

Mustafa Su.

  • 0
    TI__Guru**** 191886 points
    HI Mustafa,
    From a high level I think it is a plan that should work. You use the CNV as a trigger input to the MibSPI to start the transmission for the previously converted data. Once the data is received you use the DMA to transfer to the buffer RAM for later processing. You will need to work out the timing that is demanded by both the LTC2323 and the LC4357. For example, there is a min 9.5ns quite time from CNV falling edge to the falling edge of SCK. Make sure you select falling edge in the TRIGEVTx register. Since the MibSPI is a master it will use its own clock to sample the incoming data. I guess you will leave the LTC2323 CLKOUT unconnected, right?
  • 0 in reply to Charles Tsai
    Prodigy 20 points
    Hi Charles,

    My plan is exactly same as you briefly explained. I will start to process the incoming data when 16K data is available on the buffer RAM.
    I think if i select the falling edge in the TRIGEVTx, the time to start SCK will be much more than 9.5 ns so it will be compatibale with ADC.
    And as you say i will use SCK to sample the incoming data so i will not use CLKOUT signal.
    As i read event trigger subject , i must not use it in oneshot mode in order not to interrupt my software.

    And i want to add that i could not find an ADC that gives previous conversion in TI converters. I dont know why?
    There are some ADCs that are compatible with TI DSPs buffer serial ports but i could not find an exact low speed ADCs with SPI interface than i can use it with Hercules. Maybe i must make more search but at this point Linear Techs ADC is fine for me.

    Thanks very much.

    Mustafa
  • 0 in reply to Mustafa Su
    TI__Guru**** 191886 points
    Hi Mustafa,

    Yes, if you use one shot mode then the transfer group will be disabled after the transfer is finished. So you don't want to use oneshot mode.

    I will also suggest that you post your question to TI Precision Data Converters forum as to which TI ADC converter will best fit your need.
    e2e.ti.com/.../73