To add on to what Nathaniel said, You must ALWAYS Do XSCREEN 2 in your program to switch the Keypad on the Lower Screen to Nothing. Display 0 and Display 1 switches between what The Program is using.
For examples,
Display 1
Print "Hi
SPSET 0, 1
Puts "Hi" and a sprite to the bottom screen. To switch back to the top screen, say DISPLAY 0.
0そうだね プレイ済み