AnsweredAssumed Answered

AD9851 Initialization

Question asked by EugeneG on Jan 10, 2013
Latest reply on Jan 18, 2013 by Georgy

Hi, i am trying to program  DDS AD9851, but i can’t start output frequency generation.

I use 20 MHz generator as reference clock and 6x multiplier to get 2 MHz output.

According to the on-line calculator http://designtools.analog.com/dt/dds/ad9851.html  i got following values “W0 0xBA”, “W1 0x62” “W2 0x22” “W3 0x20” “W4 0x80”.

I made hardware configuration for serial load enable word W0.

To reset DDS default values i make this  workflow:

1)pull up Reset line;

2) 10 microseconds  delay;

3) pull down Reset line;

4)pull up W_CLK line;

5)pull down W_CLK line;

6)pull up FQ_UD line;

7)pull down FQ_UD line;

// reset device and enable serial load mod;

8) pull down Serial line and make for 40 times pull up/down W_CLK line;

9)pull up FQ_UD line;

10)pull down FQ_UD line.

 

To load calculated data (w0-w4) i make this workflow:

1)pull up Reset line;

2) 10 microseconds  delay;

3) pull down Reset line;

4)pull up W_CLK line;

5)pull down W_CLK line;

6)pull up FQ_UD line;

7)pull down FQ_UD line;

// i resetting device to clear phase accumulator +phase offset and then re enable serial load mode

8) transmit W0-W4 by right shift in series and sending current byte lsb.

9)pull up FQ_UD line;

10)pull down FQ_UD line;

Оn oscilloscope i see that the right data load to the DDS,but i don’t see any output generation. Could you check my workflow for errors please.

Outcomes