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ADS131E08: About RDATAC and RDATA

Y.Ottey
Mastermind 6145 points
Part Number: ADS131E08

Dear all,

I would like to ask about RDATAC and RDATA mode.

I looked at the data sheet, but I couldn't confirm the following, so I'd like you to let me know.

(1) How long is / DRDY cycle in RDATAC mode?
(2) How many SCLK cycles from command transmission to data output in RDATA mode? (Or how long does it take from command transmission to data output?)
(3) In RDATAC mode, there is a data read prohibition time. Is it not RDATA mode?

Best Regards,

Y.Ottey

  • 0
    TI__Guru* 98005 points

    Hello Y.Ottey,


    I'll just answer your questions, but first, let me explain a little more about how RDATAC and RDATA work. First, there are two modes of reading the data from the device they are different in terms of how data is loaded into the DOUT register. One mode is read data continuous RDATAC. In this mode the ADC data is loaded to DOUT every time there is a /DRDY indication. You use /DRDY to determine when to read the data. Note that you have until the next /DRDY indication to fully read the data, because DOUT is automatically updated at the next /DRDY indication. If you're halfway into reading the data, and there is a new /DRDY, you would get corrupted data. The second mode uses the stop read data continuous (SDATAC) with read data command (RDATA) to read the data. For this mode, you won't get interrupted by new /DRDY when reading the device. The DOUT is updated only when you send the RDATA command.

    Going back to your questions:

    1. The /DRDY cycle is exactly the same as the data rate of the device. If the data rate is 8kSPS, then the /DRDY indications will come every 125us. This is the same in RDATAC or SDATAC modes.

    2. The read from RDATA would be 8 bits for the RDATA command plus the 24 bits for status plus the bits for all the channel data. If the device is putting out 24-bit data for all 8 channels, this is a total of 224 bits.

    3. There is not data read prohibition time for RDATA mode. This is because using the SDATAC and RDATA, DOUT is only updated when the RDATA command is set. With RDATAC, the /DRDY can interrupt the output data read.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Mastermind 6145 points

    Hi Joseph

    Thank you for your reply.

    I would like to ask more question about your answer No.2.

    According to the data sheet, if the Start pin is set to High and an RDATA command is sent, Satus and N-channel data will be read.

    As shown in the figure below, it can be read when the RDATA command is sent and Status + N-channel Data is read at the next SCLK.

    When operating in RDATA mode, it is good to recognize that Status and N-channel Data are read immediately after the RDATA command is sent (from the next SCLK) if the Start pin is high as shown below?

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru* 98005 points

    Hello Y.Ottey,

    First, the START pin is used to start ADC conversions. After the conversion completes, then the data can be read. If you want the conversions to continue, then you can keep the START pin high. If you do not need the conversions to continue, then you can pull START low. After the /DRDY indicates the last conversion, you can still use RDATA to read the data from the device.

    When operating in RDATA mode (not in RDATAC mode), the RDATA command can be immediately followed by the read of the STATUS and ADC data with the clocking of SCLK.

    Did I give you the answer you needed? I'm not sure I understood what you asked in your question.

    Joseph Wu