OK, so just one pin that I know of…
I have a application I was using that has been running as intended.
All of a sudden I was no longer receiving messages on my 16X2 SerialLCD (A Sparkfun 3,3 Volt).
I found that the TX Pin on the Quad RS232-HS C register is bad.
TX low voltage is 1.666 - TX high is 1.892
I have connected nothing but the SerialLCD RX pin to Socket 3 (IKU X) Pin 4.
Just a comment. Not hate mail.