Use the XTAL command to change the value of the simulated external oscillator. This in turn affects the input to the PLL/DCO, and therefore the bus frequency. The P&E simulator is a cycle-based simulator, so changing the XTAL value does not affect the speed of simulation. It does, however, affect the ratio in which peripherals receive cycles. Certain peripherals that run directly from the XTAL will run at different speeds than those that run from the bus clock.