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Programming the AD9951

Question asked by makob on May 11, 2017
Latest reply on May 18, 2017 by LouijieC


I have tried for several days now, to get any response of my DDS-Chip AD9951:

My goal is to get a frequency at the IOUT Pin, determined by the FTW.

I want to program the AD9951 with an XMega by using the USART (in SPI Master Mode, so I use SCLK and SDIO).

For programming the DDS-Chip I use following steps:


1. write register address on SDIO (e.g. CFR2: 0x01)

2. write all bytes to SDIO (e.g. CFR2: <23:16>,<15:8>,<7:0>)

3. repeat step 1 & 2 to write to each register

4. wait 200 us to be sure data is transmitted

5. write a high to IO Update for 1us (witch is about 6 rising edges of SYNC_CLK)


If I understand that correct, the AD9951 writes at the rising edge. In that case the SCLK an SDIO looks as it should be.


I feed the REFCLK with a 20 MHz MEMS Oszillator and I can measure a frequency of 5 MHz on the SYNC_CLK Pin, which is the normal characteristic.


So in my opinion writing data to the AD9951 should work. But the DDS doesn't react to anything.

I always measure 5 MHz on SYNC_CLK and some noise on IOUT. I've tried to set the SYNC_CLK Pin to a logic 0 by writing 1 to CFR1<1>, but no reaction.


I have no idea what i could try next. Can anyone help me please?


The circuit of the AD9951 is described in the pdf.