logic input that can handle a higher voltage but output a low voltage?
How to make a low-speed digital input tolerant against voltages > Vdd:







simulate this circuit &ndash; Schematic created using CircuitLab

Ignore anything but 0V on the input. That's what the diode does. Pullup to +Vdd if not 0V. If the IC has a built-in pullup (e.g. TTL behaves this way, and also many µC) you can leave out the external one.