schmidt trigger

can someone please tell me if you use a schmidt trigger sn74ls14 with a 6v input through a 1n4005 diode , will the max output be 5v. I am hooking it up to a sst89c54 microcontoller chip and don't want to blow the port. The signal is coming off a speedometer. Any help with the calculations to find the speed to display on an lcd will be appreciated

You can use opto-coupler for added safety or simply use the circuit attached below. The zener will protect your port even if input voltage is greater than 6V.

In this case You can omit the serial diode, because the zener also protected against reverse voltage.