Hi Di - so you are comparing these two images below?: 1 - before SPI: 2 - after SPI: I wonder if this is caused by how your MCU has configured the pin connected to the ADS1299 /DRDY. It seems to be loading the pin and pulling it high. As mentioned earlier, the /DRDY pin should idle low if no data is read from the device. Otherwise, if there is activity on SCLK, the first SCLK falling edge will clear the /DRDY interrupt on the ADS1299, such that it returns high and waits for a new conversion. Regards, Ryan
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