Stand Alone ATmeaga328P Serial Port Issue Arduino IDE


I was using Arduino Pro Mini (with ATmega328P chip on) for my serial communication project. Now I bought a stand alone ATmega328P and use Spark Fun Bus Pirate to program the stand alone ATmega328P since I still want to maintain the Arduino IDE. I successfully flash the program to ATmega328P . However the serial port behaves strangely.

I sent AT,at,Hello World, Hello World correspondingly but it returns

Send Return Expected
AT !õá AT
at !÷ at
Hello World H%‹ëªo"‹{FF} Hello World
Hello World H-‹ëªo"‹{FF} Hello World

I set up the baud rate at 9600 on Pro Mini

Now while I tested out on the stand alone ATMega328P I used both 115200 and 9600 both gave me the same result.

Anyone knows what issue the could relate to?