AFE4490: Trouble Getting any MISO data/ inability to read from AFE4490

Joseph Sottosanti

Part Number: AFE4490

I'm also having trouble reading from the AFE4490 chip. I'm using a header pins on a Jetson Xavier NX to connect to the ProtoCentral AF4490-based Pulse-oximeter shield, and programming the SPI communication using python spidev. I am able to write to the shield and see the appropriate data on the MOSI line, but I am unable to get anything on the MISO line. Here is my code:

def afe44xxRead(address): #-> list:
    """
    Reads data from address on AFE module
    """

    data2 = [0,0,0]
    SPI.open (bus, device) # open SPI bus 0, device (CS) 1
    data = 0X000001
    top = (data >> 16) & 0xFF
    middle = (data >> 8) & 0xFF
    bottom = data & 0xFF
    SPI.writebytes2([CONTROL0,top,middle,bottom]) #enables diagnostic mode for reading data
    data2 = SPI.xfer3([address, 0x00, 0x00, 0x00]) #reads data back 0x00, 0x00, 0x00
    SPI.readbytes(3)
    SPI.close() #(0,0) # close spi device
    return data2 #return with 24 bits of read data

Where, address is LED1VAL = 0x2c.

These are the results I get on the oscilloscope:

writing 0x000001 to CONTROL0:

And here is the result from the SPI.xfer to get data back from the LED1VAL:

And the result from trying to use the read function:

Am I understanding the correct method for trying to read data from the AFE chip? My understanding per the data sheet is that you need to write 0x000001 to CONTROL0, and then send the address of whatever pin you want to read from (in my case I'm trying to do this from LED1VAL). I noticed in the reading data section of the data sheet it says "specify the SPI register address with the desired content to be read". What is meant by "desired content"? What else do we need to send along with the address to be able to read?

Any help would be greatly appreciated!

Thank you,

Scott