AD1933 SPI Communications

Hi Everyone,


I have been struggling with an issue now for some time and I have not been able to figure out what I need to do to get this to work properly.


I am using the AD1933 along with an Atmel 32bit microcontroller (3.3V I/O). I send data to the AD1933 over the SPI control port, but I do not ever see a response on the MISO line, and I don't know if the DAC is actually accepting any of the data that I am sending to it.


I am setting CLATCH low, and then the tx data is valid on the rising edge of CCLK. CLATCH has a 10k pullup resistor connected to it. The RST has a 10k pulldown resistor attached, it is driven high after a delay of 1s after the MCU is configured. The CCLK is operating at 705.6kHz and XI is driven by the MCU at 256x44,100kHz (11.289MHz)


I am trying to write to register 1 (PLL & Clock Control 1), and then read back the data after 10ms delay. MISO (not shown in my captures) seems to remain low. The data I am writing to MOSI is 0x080198 and then 10ms later 0x090000.


Things I have tried:

1. Change the operating mode of the SPI (clock polarity and edge).

2. Swap the DAC for another in case the chip was bad.

3. Change frequency of CCLK to different values

4. Pullups/pulldowns on MISO, also disconnect MISO from the MCU and allow it to float.

5. Try writing to a different register, and different data values on MOSI.


Here are images from my scope, please excuse my ancient technology




Thanks for any help!!

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