// Fill screen with smiles
LDA #97 // Smiley face
STA BackgroundSprite
CALL FillScreen

LDA #98 // Sad face
STA BackgroundSprite
CALL FillScreen
HLT

FillScreen: LDA #63 // Copy BackgroundSprite into 0-63
STA i
ScreenLoop: LDA BackgroundSprite
STA ~i // indirect addressing (i stores an address)
LDA i
SUB #1 // decrease address
STA i
BRP ScreenLoop // repeat for each screen cell
RET

ORG 69 // set next memory address to 69 (after screen and buttons)
BackgroundSprite: DAT 5
i: DAT 63