OK, getting off subject after I said it is too early to start talking abut software....
However, I do have reason to ask about configuring the I/O pins.
I am still thinking about hooking up HC-05 to MY nanoVNA which does not have dedicated P3 pins.
To do that I need some room to add wires directly to the CPU and if such room is not available near CPU pins 30/31 I'll will be looking for other pins.
BTW
I agree that EIA can be intimidating , but after all it is all about options, no magic involved.
I am not sure I share concerns about I/O speed, my first encounter with the EIA was @ whopping 110 bauds.
Years ago I got professionally involved communicating with a device of unknown options - so one of my "for hire " C code was to
run thru all of the options until intelligent / readable response was received
..and if the communication is too slow , then there is more time for cup of coffee...
