DDS (generating sine waves) with onboard DAC using latest PIC 16F chips?

[HankMcSpank]

Ok, so I am now up to speed with you who is up to speed with me. We can now plod along blindly together - LOL. I was thinking of doing this all with software so as not to be dependent on HPWM. Chasing the single low cost PIC for 1 purpose, I was assuming HPWM may not be available.

Quick question, what is the fastest time needed? ie, 5,000hz has a time of .2mS, but 5,000.01 has a time of .199999mS. so you want .1uS, .01uS,1uS,bla bla bla. on the other hand 100hz is 10mS while 100.01Hz is 9.9999mS.

As you can see, I am having conceptual trouble here with the .01Hz spec.

Maybe I'm too ambitious with the .01Hz accuracy, maybe .1hz is more achievable (initially)....as it goes, I actually only need that accuracy at the lower end of the 60hz-5,000Hz frequency range (where obviously 0.1Hz error of say 60hz is a whole lot more in percentage terms than .1Hz for 5khz) but with DDS you have to decide on the acceptable resolution then be stuck with it across the frequency band. so yes, say 50.01Hz, 50.02Hz, 50.3Hz thru 5,000Hz is what I hope to achieve here.

I've read that DDS 'interrupt rate' should be at least twice the targetted/required highest freqency, which since I want 5Khz, should mean a minimum interrupt of 10khz...but I thought 20Khz might be better. So with a 16 bit accumulator, we get....

audio ouput frequency granularity = 20,000/65536 or 0.31hz (which is not enough) ...even dropping the interrupt rate to 10khz means granularity of 0.15Hz)

That said, for proof of concept, maybe I just go with that initially ....ie 10,000 interrupts per second and a simple 16 bit accumulator - once that's been proven, then we can stride out a bit!