GoForSmoke:
The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSRnB Register.
I get that, which is done in HardwareSerial.cpp towards the bottom of begin() with the line below:
sbi(*_ucsrb, _txen);
That _txen is a local variable to HardwareSerial that's passed in through the constructor as in my first post above. I'd like to catch where that value is coming from. The default behavior when calling Serial.begin(baud) will turn TX on with that line above because _txen == 1. I'd like to make _txen == 0 all the way back to the source but I just can't find where that is.