AD8285 SPI ISSUE

We have been trying to read/write to AD8285 using SPI & its not working ( see below detail)

Based on the datasheet we pulled CS low & provided 16Bit control/Address data & provided addition 8 pulses of clk to read data. We are always reading '0'. See attached picture.

1. First picture yellow is SCLK & green is SDIO.

 

2. Second picture shows CS & SCLK timing.

We have connected below pins to ground as we were planning to use SPI for configuration.

1. MUXA

2. ZSEL

3. AUX

Kindly provide help.

Thanks,

Rakesh

  • To add further information:

    1. Verified all the supply pins & Rbias pin is showing 0.51V.

    2. Data bits are toggling.

    3. DSYNC is always low ( we expected it be high at start of each frame, as per data sheet).

    4. Part number is AD8285WBCPZ.

    5. SDIO direction is changed to input while reading data.Still clueless why device is not putting data on SDIO pin.

    --

    Rakesh

  • 0
    •  Analog Employees 
    on May 23, 2016 7:59 AM

    Hi Rakesh,

    One thing to try would be to zoom in on the time axis to look for transient glitches that may show up on a scale faster than 500us/div.  I see some evidence of this in the areas that should be flat in your scope captures.  Occasionally, some of the small glitches are much bigger when viewed on a faster time scale.

    Regards,

    Paul

  • Hi Paul,

    I checked for any glitches/spikes, waveforms are clean after zooming also(reducing x-axis time).

    Below are the strange observation:

    1. Single byte read not working (while setting W0,W1 both bits to  0).

    2. Single byte read( but provide 16 bit clock ), result is not consistent.

    3. Two byte read(W0=1) works & it gives content of address & address-1.

       a) why someone design to give content of address & address-1, instead of address, address+1

    --

    Rakesh

  • 0
    •  Analog Employees 
    on Jun 13, 2016 10:14 PM

    Hello Rakesh,

    Thanks for the inputs. I will set it up and check whether I can replicate your observations. I will get back to you soon.

    Kris

  • 0
    •  Analog Employees 
    on Jun 14, 2016 8:12 PM

    Hello Rakesh,

    I tried a single byte read through SPI and I am able to read the address on the line. I also tried a read with the ZSEL, MUXA, and AUX pins low, and the SPI readback is still working. If I am not mistaken, you are trying to do the same thing on Register 0x01.

    I noticed that your SCLK frequency changes during the readback of the address. Are you able to adjust this so that it is consistent throughout the data stream?

    Thanks,

    Kris