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ADS1278-EP: DOUT1 pin connection to controller and parallel port communication detail

navin singh1
Prodigy 200 points
Part Number: ADS1278-EP
Other Parts Discussed in Thread: ADS1278, ADCPRO, ADS1278EVM-PDK

Hi Team,

I was going through the Application note for ADS1278, and found one schematic of ADS1278 Evaluation board. The DOUT1 of ADS1278 is  connected to input of SN74LVC2G74MDCUTEP.Also the CLK of  SN74LVC2G74MDCUTEP is getting inverted input of SCLK. 

If you could help me understanding this circuit, I mean cant we directly use the DOUT to SPI MISO of controller without FF and inverter.??

Also how can I use DOUT1 to DOUT8 to receive data Parallel to my Controller.

Thanks and regards

Navin Singh

  • 0
    TI__Genius 14540 points

    Hi,

    I will look into your questions on the ADS1278.  Could you please let me know the literature number of the application note you reference.

    Thanks

    Christian

  • 0 in reply to Christian Yots
    Prodigy 200 points

    Hello Christian,

    The literature no is SSBAU324–September 2018, ADS1278EVM-CVAL Evaluation Module User's Guide. 

    Thanks,

    Navin

  • 0 in reply to navin singh1
    TI__Genius 14540 points

    Hi,

    I reached out to the team that developed this product and got the following information back.

    This post describes how the circuit works.

    https://e2e.ti.com/support/data-converters/f/73/p/482598/1741358https://e2e.ti.com/support/data-converters/f/73/p/482598/1741358

    Depending on the number of channels and the maximum data rate, you may not need this circuit.  For the EVM, the DSP needed to capture data on the rising edge of SCLK, and to support the maximum data rate where all 8 channels of data are shifted out on DOUT1, the additional flip-flop and inverter were needed.

    This circuit captures DOUT1 on the falling edge of SCLK (which is why the inverter is needed), and then the DSP captures the output of the flip-flop on the following rising edge of SCLK.  Data capture on the falling edge of SCLK is required at higher SCLK rates to meet both the t-dopd and t-msbpd specifications.

    If you do not need to sample at the maximum data rate, then you have more time to clock out the data and can use a slower SLCK.  If the clock is slow enough to leave enough time between the falling edge and next rising edge of SCLK to meet the t-dopd and t-msbpd specifications, your host processor can capture on the rising edge and meet the ADS1278 requirements.  Also, if the host processor can capture data on the falling edge of SCLK, you may not need the additional flip-flop at the higher data rates provided the setup and hold times of the host MCU are met.

    If the customer wants to use the device in Discrete Data output mode (tie the FORMAT pins to 010 for SPI Discrete), you can run SCLK at 1/8 the master clock frequency and can easily meet all of the timing requirements at maximum output data rate without the addition of the flip-flop and inverter.  Just to be clear about the Discrete Data output mode, you are receiving 8 bits of data for each SCLK.   However, this data is effectively 8 serial outputs, one for each converter channel.  The customer would need to unpack the data, or use 8 individual SPI ports that share a common SCLK.

     If the customer can provide the exact operating conditions they would like to use, output data rate, SPI/Frame-sync, number of channels (I assume 8) and MODE, I can provide a specific example.

     Thanks,

    Christian

  • 0 in reply to Christian Yots
    Prodigy 200 points

    Hi Christian,

    Thanks for the explanation.

    I am using SM320F28335 Digital signal controller and interfacing it with ADS1278. 

    Can you provide me some example code for SPI interface between both. And the sampling rate I would be needing is max 50Kbps

    Also while using the above mentioned controller, I don't need to use the flip flop and inverter circuit??

  • 0 in reply to navin singh1
    TI__Genius 14540 points

    Hi,

    If you do a search in E2E on "ADS1278 SPI" there are several previous posts that address SPI code including the following:

    https://e2e.ti.com/support/data-converters/f/73/t/813910?tisearch=e2e-quicksearch&keymatch=ads1278%20SPI

    As stated here, the installer for the software available on ti.com now includes example source code.  To my knowledge there are no other example codes available other than what is provided here.

    Thanks

    Christian

  • 0 in reply to Christian Yots
    Prodigy 200 points

    Hi,

    I was searching SPI code for interfacing ADS1278 with my controller SM320F28335.(SPI interface)

    one of your post suggested me to download this software and install it from http://www.ti.com/tool/ADCPRO.   After installing the software I was unable to find the path C:\Program Files (x86)\ADCPro\plugins\evm\ADS1278\source.

    As there was no folder after C:\Program Files (x86)\ADCPro\plugins\evm naming ADS1278.

    Can you help me with this.

    Also if possible can you mail me the code at navinksingh@eaton.com

  • 0 in reply to navin singh1
    TI__Genius 14540 points

    From the referenced e2e post:

    ".....you can find the link to this software on the ADS1278EVM-PDK main web page under the 'Order Now' section.

    Once you have downloaded and installed, you will find the source code in the following directory:

    C:\Program Files (x86)\ADCPro\plugins\evm\ADS1278\source"

    http://www.ti.com/tool/ADS1278EVM-PDK

    Thanks

    Christian