I am able to initialize the device in single-tone mode and load a FTW and see the desired signal
at J4 on the evaluation board.
My question is related to how I'm writing the FTW to the profile register (x0e).
With Fs = 500MHz, I need to write x33333333 for the FTW to see a tone at
100MHz. This happens to be convenient since I write the same hex value to
each register. When I tried to generate a 60MHz tone, I calculated the FTW
to be x1eb851ec, but I did not see a signal at the output when I loaded
[31:24] = 1e
[23:16] = b8
[15:8] = 51
[7:0] = ec
for the FTW. After playing around with the different combinations, I found that writing
[31:24] = e1
[23:16] = 8b
[15:7] = 15
[7:0] = ce
generated the desired tone. This reversed on a nibble boundary, but from the description
on page 51 of the datasheet (rev B.) there's no indication that this type of swap is needed.
Is there something I'm missing? Are there other registers that need to written in this manner?
I'm using the on-board 25MHz xtal, so given that I need to enable the pll and provide a multiplier
and FTW - x33333333 generates the right tone, I don't think that there is an issue with order
in which I write the bits to the register, but I'd like to confirm that the behavior I'm seeing is
to be expected.