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9959 autoclear phase accumulator

Question asked by Zirbel on Oct 24, 2012
Latest reply on Oct 31, 2012 by Zirbel

I want to clear the phase accumulator every time I update the relevant profile pins for the appropriate channel while operating in FSK mode.  For 2-level FSK, this mode seems to work. That is, I can select between the two frequencies by changing the state of the profile pin and, looking in the time domain, I observe that the phase of the output resets upon each relevant profile pin state change.  When I change the channel to FSK 4-level, again using the same "autoclear" option, I observe that I can select 4 frequencies using the appropriate profile pins but the phase doesn't "clear" for any state change.  Additionally, FSK8 and FSK16 modes do not autoclear the phase either. What I want to know is: Should I expect this behavior, or is there another option for the higher level keying that will clear the phase when toggled? The data sheet (Rev.B page 27) makes no mention of any difference between 2/4/8/16 level autoclear.  Thank you in advance.


Input clock: 100MHz (using the 4x multiplier to get to 400MHz)

Communication: 2-wire


Attached is the serial data (read by an SPI sniffer) for the different modes. As you can see, the serial data is almost identical between the 2-level and 4-level modes, however, the behavior of the 9959 is not the same in terms of autoclear phase.  I haven't decoded it, and it may be bit-shifted/reversed, but the 13th byte from the left is changing from (c1) (for autoclear) to (c0) (without autoclear) (probably is the CFR[2] bit). The 6th byte changes from (40) for 4-level to (00) for 2-level which is probably the appropriate bit for the FR1[9:8] modulation level bits.