I finally made my first flight three weeks ago. For the first five flights, my transponder displayed the correct pressure altitude. During the last four flights, the transponder showed an up or down arrow if I was climbing or descending, but the altitude only shows the initial field elevation, i.e. FL009. Serial port 1 is set to AVTN/ICARUS.Is there a way to see the output on the serial port to see what the 4500 is sending to the GTX?