Daisy and main board sample synchronization

chesswebchessweb
edited August 2015 in Cyton
On the 32-Bit board, pin 47 of the ADS1299 (labeled DRDY) goes to DRDY of the PIC controller.  I don't see how that is implemented on the daisy board. There pin 47 of the ADS1299 (labeled _DRDY) is not connected to anything. How does that make sense?

Comments

  • chesswebchessweb
    Never mind. I checked the ADS1299 docs and there DRDY of the chained device is left open.
  • adminadmin
    neverminding...
    ;)
  • biomurphbiomurph Brooklyn, NY
    Yes, we are relying on the DRDY signal from the ADS on the main board to tell when the data is ready.
    To synch the two ADS chips, we select both ADS1299 ICs on the SPI bus by pulling both of their CS pins low,
    Then we send the START command.
     Because they are both sharing the same clk (Daisy Module clk driven by the OpenBCI 32bit Board ADS clk)
    We can be sure that the data from both is sampled simultaneously. 
  • AgustinSAgustinS
    edited August 2015
    Hello everybody.
    I am designing a EEG/EMG adquisition board and I'm thinking in a design similar to openBCI. I'll use the ADS1299.

    I have a doubt related to the 16-channels configuration (openBCI board + daisy chain board) and if it is possible to adquire the
    16 signals simultaneously. I see that the configuration is not daisy chain but it is the standard mode documented in the data sheet.
    Each ADS1299 chip has an Chip Select signal. My question is: how do you give the START to the chips to start the convertion at the same time?
    Is it possible? Or one of them start earlier than the other?

    Thanks!
  • AgustinSAgustinS
    Thanks wjcroft!
  • AgustinSAgustinS
    I have a question about data retrieval
    After the signal DRDY of the main board indicates that data es ready (data is supossed to
    be ready in both boards), how do you send data to the microprocessor? Do you first select one of the ADS1299 chips to
    get data by SPI and then the same for the other chip?
  • biomurphbiomurph Brooklyn, NY
    We are using separate CS pins for each of the ADS1299 ICs so that users can elect to change the settings on each chip and all channels if they like.
    The Daisy ADS is clocked by the main board ADS CLK output, which keeps them in sync. When we start the data acquisition, we select both ADS chips' CS pins to send the START command. Because we're not expecting anything on the MISO line, it is possible to do this.

    When the DRDY pin is asserted by the main board, we retrieve data from the main and then the daisy boards.
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