See http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
JP2 is in the center and allows you access to the 16U2 port PB4..PB7
Which does not answer the "Why" question ...
See http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
JP2 is in the center and allows you access to the 16U2 port PB4..PB7
Which does not answer the "Why" question ...