# How to calculate the A/B counters in a Frac-N PLL?

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#### bolton00

##### Newbie level 6
I have a PLL with a fixed Prescaler 32/33. The dividing ratio is calculated by:
Code:
N = 32B + 33A
What's the most efficient way to calculate the A and B values, knowing that both A and B are 10 bit registers. I need to implement this algorithm on a MCU, thus the request for efficiency. Example given in the PLL datasheet:
Code:
R: 200kHz, N: 4335: 54*32+79*33 =>867MHz

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