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Fill.asm
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Fill.asm
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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.
(BEGIN)
// if KEYBOARD == 0 jump to white else jump to black
@KBD
D=M
@WHITE
D;JEQ
@BLACK
0;JMP
(DRAW_LOOP)
// i = 8192, addr = 16384
@8192
D=A
@i
M=D
@SCREEN
D=A
@addr
M=D
(DRAW_LOOP_BODY)
// if i == 0 jump to begin
@i
D=M
@BEGIN
D;JEQ
// D = R0 (color to fill)
@R0
D=M
// A = addr, [A] = D (R0)
@addr
A=M
M=D
// addr = addr + 1
@addr
D=M+1
M=D
// i = i - 1
@i
D=M
D=D-1
M=D
@DRAW_LOOP_BODY
0;JMP
(BLACK)
// R0 = -1
@R0
M=-1
@DRAW_LOOP
0;JMP
(WHITE)
// R0 = 0
@R0
M=0
@DRAW_LOOP
0;JMP