I thing you are referring to a GLCD. A GLCD initializes itself on power on, you will have to send a few command to start using. You have to note that there are two controllers on board, each controlling one side of the screen. Do you have your GLCD's datasheet? Well here is the link to a code in C you may find useful:https://ccrma.stanford.edu/courses/250a-fall-2003/docs/avrlib-new/glcd_8c.html .