Content originally posted in LPCWare by svenb on Thu Jul 02 07:33:40 MST 2015 Hi!
The user manual for the LPC43xx parts (UM10503) states in section 12.7.5 "Fractional divider for PLL0AUDIO":
Quote: When the fractional divider is active, the sigma-delta modulator block generates divider values M and M+1 in the correct proportion so that an average division ratio of M+K/L is realized where 0<=K<=L and M, K, and L are integer values. M Is determined by the integer part of the PLLFRACT_CTRL register (PLLFRACT[21:15]) and K is determined by the fractional part of the PLLFRACT_CTRL register (PLLFRACT[14:0]). Consecutive M and M+1 values are then further encoded into appropriate MENC values before being presented as input to the M-divider.
But what is L? One might assume that it is 2^14, but apparently that's not it. Am I overlooking something obvious or is that just not mentioned anywhere?
Content originally posted in LPCWare by svenb on Thu Jul 02 09:46:00 MST 2015 Ah, stupid me, it's 2^15 of course, not 2^14. Still, I think this should be mentioned somewhere, just "M, K, L are integer values" is not very enlighting.
