// 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  // 32*256  --> 32 16er pro Zeile
D=A
@ENDPOS    // in @16
M=D

(LOOP)
    @SCREEN     //Screen-Einstiegsadresse
    D=A
    @ScreenStart        // @SCREEN 16384 --> @17
    M=D

    @i          // Zähler = 0 18
    M=0

    @KBD        //24576
    D=M         // Tastatureingabe ?

    @WEISS
    D; JEQ      // WEISS WENN D == 0
    @SCHWARZ    // SPRINGE ZU SCHWARZ
    D; JNE      // WENN NICHT 0

(SCHWARZ)
    @ENDPOS
    D=M
    @i
    D=D-M       // ENDPOS -1 = 0 ?  DANN ZU LOOP
    @LOOP
    D;JEQ   

    @ScreenStart 
    A=M
    M=-1        // SETZE -1 == SCHWARZ

    @i
    M=M+1       // i++

    @ScreenStart 
    M=M+1

    @SCHWARZ
    0;JMP

(WEISS)
    @ENDPOS
    D=M
    @i
    D=D-M       // ENDPOS -1 = 0 ?  DANN ZU LOOP 
    @LOOP
    D;JEQ   

    @ScreenStart 
    A=M
    M=0         // SETZE 0 == WEISS

    @i
    M=M+1       // i++

    @ScreenStart 
    M=M+1

    @WEISS
    0;JMP