Steve Church

question on CPU clock frequency MC9S08RE16

Discussion created by Steve Church on Aug 28, 2008
Latest reply on Aug 28, 2008 by Steve Church
I am using a 16MHz clock The manual says that the CPU operates "at the input frequency of the oscillator" so I am assuming 16 MHz. However toggling an output bit  using bclr and bset shows this takes approx 600 nS. As the bclr takes 5 machine cycles this makes each machine cycle equal to about 120nS.This shows the CPU operating at 8Mhz not 16Mhz. Is the manual wrong? It shows the CPU being driven by the output of the oscillator before it goes to the divide by 2 block which produces the bus clock.