stm32f103 14mhz adc clock and prescalers only allow 12mhz?

[andrewg]

hi i'm reviewing rm0008 ref manual for stm32f103 the adc.

accordingly, adc clock max is 14mhz and it takes 14 adc clock cycles for 1 conversion - hence 1msps per ADC.

however, from the RCC section the available prescalers are 2, 4, 6, 8

and if we take 72mhz / 6 that gives 12 mhz

and if we assume it still takes 14 adc clock cycles per conversion, that gives

1m x 12 / 14 ~ 857ksps per adc?

does it still takes 14 adc clock cycles per conversion if the adc clock runs at 12mhz?

in addition, it seemed there isn't really a feasible way to achieve 14mhz on the adc clock ?

thanks

[Tesla DeLorean · Accepted solution]

>>in addition, it seemed there isn't really a feasible way to achieve 14mhz on the adc clock ?

You clock the F1 at 56 MHz?

[andrewg]

i see, unfortunately if the F1 is clocked at 56 mhz, usb may not work, as 72 mhz x 2/3 (prescalers) = 48 mhz which is needed by usb.

it seemed this could be a compromise of sorts

thanks for the cool and quick response. i'd make do with 12mhz on the adc clocks