It's really not difficult at all once you understand the DDS serial message
structure. I did it in PICBasic with a 14F675 and a AD9850 DDS for my HF Lab
System, including a 9600 baud software UART and a few routines that do
analog capture and log detector calibration
(http://mysite.verizon.net/jdrocci/). The whole code footprint was about 600
words if I recall, and it could be much smaller if it were coded in
assembly, as the Basic compiler loads a number of subroutines that don't
always get called. If you're daunted by the math involved, PICBasic might be
the way to go as it includes multiply & divide capabilities.

Joe
W3JDR


"Ken Scharf" wrote in message
...
Has anybody here attempted to use a pic to control a dds chip (and
wrote the software himself)? I was looking at G3XJP's article on
his 'pic-n-mix' vfo using an 16C84 to control an AD9850. I can't
belive he was able to get all that functionality into just 1k of
code and 64 bytes of eeprom. (you can find his article as an apnote
on the Analog Devices web site ... AN-557 is the number)

I'm thinking of using the AD9954 dds chip instead of the 9850.

I'm just starting to look at what's required in code to get from
a BCD input to the DDS word. Keep in mind G3XJP didn't hard code
his clock as a constant, it can be adjusted. The formula to
get the DDS word involves some math with fractional parts, it can
be done in interger math with some scaling or lookup tables, but
there isn't much room in a pic. I just ordered some 16F88's with
4k of program space and 256 bytes of eeprom so I would have a little
more room.

Any starting ideas would be welcome!