Single bit digital control from FPGA to DDS?

[JCard]

I am trying to control a Direct Digital Synthesizer driver from AA optoelectronics (Model DDSPA) in order to generate different frequencies for my acousto optic deflector. The only guidance I have found on this has been from the AA optoelectronics website:

8 BITS FREQUENCY CONTROL (15, 23, 31b) A byte (8 bit //) controls the frequency of the output RF signal. A D/A converter converts the 8 bits command (N) on an analog signal which controls linearly the output frequency. 256 steps are available : refer to your test sheet for pin connections. - When N=00000000, RF signal frequency = F minimum - When N=11111111, RF signal frequency = F maximum

.....The driver has a DD44HD connector, which I have wired up the 15 bit control to my FPGA digital input using a screw terminal board. I want to be able to generate a sweep through the frequencies, however, I am unsure how to go about this. Do I need to generate one signal and send it to each of the 15 pinouts, or have each pinout be a boolean and switch them to true and false through some sort of loop? Thank you for any guidance. 

[jesicadiaz]

Hi JCard, 

Have you tried any of the approaches you suggested? If so, what were your results? 

I found a paper related to this issue that could give you some guidance. Please check it our and let me know if it helps you! 

Regards! 

[Conner.A]

Your idea of sending a boolean to each pinout in a loop is a good start. Let us know how it goes so we can help troubleshoot!

Conner A.

Applications Engineer

National Instruments

[MaxJoseph]

Can you clarify your setup? Do you use the DDS to generate the 8 bit frequency control and send this to the FPGA or do you use the FPGA to generate the frequency control and then send this to your DDS?

I assume that the latter is true, and you mistakenly typed FPGA digital input when you ment output. Conner.A has the right idea when they say you should make a loop that that will increment a value and output this to the digital out at each iteration. Consider using a U8 and number to boolean array then breaking the array out to the digital output controls. The other 7 pins probably control other aspects (amplitude etc) of the DDS and the data sheet will help you in determining what these should be. 

Have fun and let us know how you get on. Post code!

[JCard]

Updating this post after a long while, this project sort of got put on the back burner! I have attached my code, however its still not working. I have the pin connections hooked up correctly from my FPGA connector box to my DDS, and the code compiles but is still not working. Maybe I'm not understanding how digital control works within the FPGA module? Any advice is appreciated!