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.