In cases when you can't read anything on the LCD display or only black boxes are present it is needed to adjust the contrast. This is done by setting the P0 trimmer which is located tear the top left corner of the LCD.
Procedure
Load a suitable application into the kit. The applicatin should show any kind of text on the LCD (e.g. demo\display) and run the terminal.
Using a screw-driver rotate the trimmer P0 clockwise or counter-clockwise until there is a readable text shown on the LCD.