'you might want to send a heartbeat to indicate tx link is active and working'

Good idea.

'why the tx once only obsession ?'

Not an obsession, I'm just trying to understand the mechanism here.

Another Question:

If an input pin is internally held HIGH and you put an external HIGH onto that pin, does the input pin 'see' the external HIGH as a state change? Or does it ignore it because it's internally held in a HIGH state already.