From the slide called "Basic PLL Operation", Fout = Fosc*N/R. Therefore, N/R = Fout/Fosc = 770MHz/10MHz = 77/1. This implies that N=77 and R=1 is a valid solution to this equation. Now because Fosc/R = Fcomp and Fosc is fixed, the maximum value for Fcomp corresponds to the lowest possible value for R. In this case, this would imply R=1 and Fcomp=10000 kHz. However, this disregards any constraints imposed by prescalers. Now it is necessary to confirm that 77 is a legal divide ratio for a 64/65 presclaer. From the slide on "Determining the N Counter Value", we see that B >= A is required for proper operation. For N=77, we calculate B = 77 div 64 = 1, and A = 77 mod 64 = 13. Since B < A, this value is illegal. Now of both N and R are multiplied by the same number, their ratio is the same, but this helps with illegal divide ratios. Below is a table showing how to do this ... Fosc Fout N R B A Fcomp Legal Divide Ratio (B>=A)? 10 MHz 770 MHz 77 1 1 13 10000 kHz No 10 MHz 770 MHz 154 2 2 26 5000 kHz No 10 MHz 770 MHz  231 3 3 39 3333 kHz No 10 MHz 770 MHz 308 4 4 52 2500 kHz No 10 MHz 770 MHz 385 5 6 1 2000 kHz Yes 10 MHz 770 MHz 462 6 7 14 1667 kHz No 10 MHz 770 MHz 539 7 8 27 1429 kHz No 10 MHz 770 MHz  616 8 9 40 1260 kHz No 10 MHz 770 MHz 693 9 10 53 1111 kHz No 10 MHz 770 MHz 770 10 12 2 1000 kHz Yes ...               Note that the smallest R value that works is R=5.  From the slide entitled "Basic PLL Operation", Fcomp = Fosc/R ⇒ Fcomp = 10 MHz/5 = 2000 kHz.  Note that the minimum continuous divide ratio of 4032, which would imply an N value of 53 and a comparison frequency of 189 kHz, but this is not the highest comparison frequency.  Because it is explicitly stated that the frequency is fixed, it is OK to operate below the minimum continuous divided ratio provided B >= A.