Thanks for the suggestion,
I now used an FTDI connector to connect the S5 of pixhawk 1. I can now see the terminal. I can also see some initial debug statements. However I am unable to type any commands on the terminal. It is as if it is stuck somewhere. I have not changed anything in Firmware.
Any idea on how to resolve this ?
You also mentioned without changing firmware, I cannot use the USB connection to login to the firmware. Which firmware do I need to use for that ?