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// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/04/Fill.asm
// Runs an infinite loop that listens to the keyboard input.
// When a key is pressed (any key), the program blackens the screen,
// i.e. writes "black" in every pixel;
// the screen should remain fully black as long as the key is pressed.
// When no key is pressed, the program clears the screen, i.e. writes
// "white" in every pixel;
// the screen should remain fully clear as long as no key is pressed.
// Put your code here.
@8192
D=A
@words
M=D // words = 8192
(KBD_LOOP)
@KBD
D=M
@FILL_WHITE
D;JEQ // if (KBD == 0) goto FILL_WHITE
@color
M=-1 // color = 0xffff (black)
@FILL
0;JMP
(FILL_WHITE)
@color
M=0 // color = 0x0000 (white)
@FILL
0;JMP
(FILL)
@i
M=0 // i = 0
@SCREEN
D=A
@pos
M=D // pos = &SCREEN
(DRAW)
@color
D=M
@pos
A=M
M=D // *pos = color
@pos
M=M+1 // pos++
@i
M=M+1 // i++
D=M // D = i
@words
D=D-M // D = i - words
@KBD_LOOP
D;JEQ // if (i - words == 0) break
@DRAW
0;JMP
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