project06 - add files

06/rect/Rect.asm

@@ -0,0 +1,41 @@
+// 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/6/rect/Rect.asm
+
+// Draws a rectangle at the top-left corner of the screen.
+// The rectangle is 16 pixels wide and R0 pixels high.
+// Usage: Before executing, put a value in R0.
+
+   // If (R0 <= 0) goto END else n = R0
+   @R0
+   D=M
+   @END
+   D;JLE 
+   @n
+   M=D
+   // addr = base address of first screen row
+   @SCREEN
+   D=A
+   @addr
+   M=D
+(LOOP)
+   // RAM[addr] = -1
+   @addr
+   A=M
+   M=-1
+   // addr = base address of next screen row
+   @addr
+   D=M
+   @32
+   D=D+A
+   @addr
+   M=D
+   // decrements n and loops
+   @n
+   MD=M-1
+   @LOOP
+   D;JGT
+(END)
+   @END
+   0;JMP