Why does SAM3x8e work only with Atmel-Ice programmer connected?

I have DIY sam3x8e pcb board based on schematics of Arduino Due. I can program it with Atmel-Ice (jtag connector) in Atmel Studio with basic serial transfer example and it works fine when the Atmel-ice is plugged in to the board. But when I unplugged it, the MCU doesn`t work. What are possible reasons for that?

I tested all the voltages across Sam3x8e power pins and they are all correct. I use a jumper to select which reset pin I want to use.

I will appreciate any advise! Thank you.

So what doesn't work about it?

Im trying to recieve serial message from sam3x8e through uart, but it works only with connected Atmel-Ice. When disconnected serial transfering stops for some reason. It doesnt start after reseting. I tried different uart ports and examples, they all works fine only with connected programmer. I tested the voltages on sam3x8e`s power pins and they are correct.

So you want serial communication to some unknown device? I am assuming this unknown device is a PC. How do you think those messages get from your board to the PC?

Solved!

Codlink, Im using usb-uart bridge for that. I just forget to connect gnd from bridge to gnd on pcb, I was just using rx - tx line. When the Atmel-Ice was connected it provides ground from pcb to PC usb port through JTAG connector, thats why it was working.

v_s_k:
Solved!

Codlink, Im using usb-uart bridge for that. I just forget to connect gnd from adapter to gnd on pcb, I was just using rx - tx line. When the Atmel-Ice was connected it provides ground from pcb to PC usb port through JTAG connector, thats why it was working.

Lol, sometimes one forgets the gnd connector.