AD9633 SPI problem


I am trying to communicate with the AD9633 on the EVAL-AD9633. I basically plugged in the board and connected an external SPI master to the USB_SDI, USB_SCLK, USB_CSB and ISB_SDO pins.

Using the recommeded jumper connection on J302 (1-2, 4-5 and 8-9) and then thus feed SPI into the AD9633. I am using a clock frequency as low as 100kHz.

However, I fail to receive any communication reply from the device.

Please see the screenshot in the attachment, for an image where I try to read out register 0x01. On the third byte, I expect the device to reply 0x90, but instead, I receive 0x00 all the time.
Puple: CSB measured on DUT_CSB (on J302)
Yellow: SDIO (measured on DUT_SDIO (on J302)
Blue: SCK (measured on DUT_SCK) (on J302).

Any idea what I could be doing wrong?

Thanks for your reply.


  • The problem was tiny spikes coupling from the CLK into the CSB line. Almost impossible to see on the scope, they were enough to cause the AD9633 to stop responding. Actually shorting R317, and thus grounding the CSB pin directly on the board allows the communication to flow correctly (and it does reply with 0x90)

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