A third technique is to optimize the output impedance of the buffer in the MCU to the wiring of the circuit board on which the microcontroller will be mounted. Since the wiring pattern of a two-layer printed circuit board itself has an impedance of approximately 150 to 200 Ohms, the impedance the buffer has to drive will be 100 to 150 Ohms when the system components to which it connects are surface mounted. BY designing the output impedance of the buffer to be in the 100 to 150 Ohms range, the MCU designers can control waveform ringing and reduce unwanted radiation.