A/D Conversion Time
When the GCLK frequency is 50MHz and the prescaler value is 49, total 10-bit conversion time is as follows.
A/D converter freq. = 50MHz/(49+1) = 1MHz
Conversion time = 1/(1MHz / 5cycles) = 1/200KHz = 5 us
以上是书中的原话,都没提到GCLK为什么是50??还有那个prescaler value is 49,怎么知道是49???