Answer:
The output impedence for all clock outputs is: 29.5ohms for 3.3V devices 22.5ohms for 5V devices Series resistance values used to reduce reflections and match the trace impedence can be calculated by subtracting the trace impedence from the output impedence. Example: 50 ohm trace impedence and a 3.3V CY2907 device. 50ohms - 29.5ohms = 20.5ohms series resistor value