cat: /dev/ttyAMA0: Device or resource busy

[yuting-0914]

hi, I have a problem. Could anyone help me, please. TT
It's really important, cause it's my graduation project.

cat: /dev/ttyAMA0: Device or resource busy
it always show Device or resource busy after enter and run cat /dev/ttyAMA0
I can't find out where the problem is.

Thx for helping me!!!!!