Hi Kenny G,
As you had mentioned in the last reply to set a single FTW before applying the POW updates as per the 2nd term in the phase equation, to do so I used DRG mode to set the 1st frequency tuning word.
For this, I programmed the start and the end frequency of DRG equal to the tuning word corresponding the starting frequency, Fstart (without starting the DRG ,i.e,keeping DRCTL low).
I then loaded the RAM with POW samples (2nd term of the phase eq) excluding the 1st zero POW value .
The resulting spectrum, however, was quite strange.
I could see a tone at Fstart contained within the LFM spectrum. The spectrum was found to be flipped exactly about Fstart (as pivot point) towards left,i.e.the starting frequency in this case lied at Fstart-B and end frequency at Fstart.
Later I loaded the RAM with the entire phase points as per the equation and keeping the Fstart as programmed like before via DRG ;this time a tone at Fstart and the actual LFM spectrum exactly shifted by twice the chirp bandwidth towards right was observed.
To double check this behavior, I programmed the DRG with a new Fstart' equal to 2B below Fstart .
Now I could get the desired LFM spectrum correctly placed at its frequencies accompanied by a tone at the new Fstart' ( = Fstart - 2B).
I do not understand this strange behavior. Should I use FTW register (0x007) to initialize the phase accumulator rather than DRG to do it?
Is it possible to to load the RAM with amplitude values and generate LFM via DRG at the same time?If yes, what could be the possible settings for the same, i.e.the order of DRCTL and IO_update and other ones which I should possibly take care of?
Thanks again.
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