Unlike previous GP3 models, the newest GP3A requires a pin on the board to be jumpered differently depending on the operating mode you want (as covered in the manual).


The pin in question is JP1-3 (on the GPMPU28 board; use pin 12 of the IC if you are using a different board like the GPMPU40).


If you connect the pin to ground, the GP3 will operate in the normal mode. In this mode, you can send commands to the board or replace its internal program (using the GP3EZ software).


If you connect the pin to +5V, the GP3 will run its internal program. By default the internal program blinks the LED which is a good self test. You can use the GP3EZ software to replace the internal program with one of your own.