With newer filters, a 1-MHz output at 1.7 V p-p is possible ... result from the 100-MHz square-wave input (channel 1). Resistor-divider circuits reduce the amplitude from rail-to rail to prevent ...

Or, using a fifth- or seventh-order switched-capacitor filter with a square-wave output ties up two I/O pins on the MCU. One output is used for the filter input and one for the filter clock.