I am planning to create a broken wire detection between a UART communication. The main idea was to check the Tx and Rx lines with a retriggerable astable Multivibrator which creates a HIGH Level on positive edges. The output of the multivibrator then goes together with the line level in an OR gate. So if the line is in idle state or sending data, it is in a HIGH state.
However, I am not sure what happens when the Rx is unconnected and I check the unconnected Rx line. Does the Rx have a LOW level (GND) then? Or does it have some unpredictable voltage level?
Maybe anyone even does have suggestions for a better approach to detect a broken wire on a hardware level?
Any advice would be much appreciated.