I have two different circuits on two different boards. The output of board A, let's say, is optocoupler based and hence, it has a pull up on it. This signal is connected to board B through an interconnect board. In the board B, I have used a Schmitt trigger inverter gate on the signal (to prevent signal chattering) before connecting it to the MCU's GPIO pin for detection.
My question is, should I place a pull up resistor on the input on the Schmitt trigger IC as well or not? If I keep the pin floating (don't add a pull up), will it cause the Schmitt trigger output to be unstable? I am thinking of a case when for some reason where there is a connection issue between two boards and the input of Schmitt trigger is left open in unknown state.
Any advice would be appreciable.