diff --git a/04/fill/Fill.asm b/04/fill/Fill.asm
index 29f6c20..4548e4b 100644
--- a/04/fill/Fill.asm
+++ b/04/fill/Fill.asm
@@ -3,9 +3,97 @@
 // by Nisan and Schocken, MIT Press.
 // File name: projects/4/Fill.asm
 
-// Runs an infinite loop that listens to the keyboard input. 
+// 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. When no key is pressed, 
+// i.e. writes "black" in every pixel. When no key is pressed,
 // the screen should be cleared.
 
-//// Replace this comment with your code.
+// excuse excessive comments here again..
+// run test with cmd line, otherwise it takes forever
+// later note: web IDE seems to render screen, local tester does not.
+// code duplication- we need to write the same code for filling black and white, but this feels wrong (code reuse)
+
+(LOOP) // main loop
+    // check kb input
+    @KBD // sel kb reg
+    D=M // load kb value to data
+    @FILL_BLACK // sel fill black
+    D;JNE // jump if key pressed (jump not equal? non-zero)
+
+    // jump to fill white if no key pressed
+    @FILL_WHITE // sel fill white
+    0;JMP // jump unconditionally
+
+(FILL_BLACK) // fill screen with black
+    // init count and pointer
+    // screen = 512x256 pixels = 131072 pixels total
+    // each word holds 16 pixels, so 131072/16 = 8192 words
+    @8192 // sel value for count (8192)
+    D=A // load 8192 to data
+    @count // sel count var
+    M=D // set count = 8192
+    @SCREEN // sel screen start
+    D=A // load screen address to data
+    @pointer // sel pointer var
+    M=D // set pointer = screen start
+
+(BLACK_LOOP) // loop for filling black
+    // check if count = 0
+    @count // sel count
+    D=M // load count to data
+    @LOOP // sel main loop
+    D;JEQ // jump to main if done
+
+    // set word to -1 (black)
+    @pointer // sel pointer
+    A=M // set address to pointer value
+    M=-1 // set screen word to black
+
+    // inc pointer
+    @pointer // sel pointer
+    M=M+1 // inc pointer
+
+    // dec count
+    @count // sel count
+    M=M-1 // dec count
+
+    // jump back to black loop
+    @BLACK_LOOP // sel black loop
+    0;JMP // jump back to loop
+
+(FILL_WHITE) // fill screen with white
+    // init count and pointer
+    // screen = 512x256 pixels = 131072 pixels total
+    // each word holds 16 pixels, so 131072/16 = 8192 words
+    @8192 // sel value for count (8192)
+    D=A // load 8192 to data
+    @count // sel count var
+    M=D // set count = 8192
+    @SCREEN // sel screen start
+    D=A // load screen address to data
+    @pointer // sel pointer var
+    M=D // set pointer = screen start
+
+(WHITE_LOOP) // loop for filling white
+    // check if count = 0
+    @count // sel count
+    D=M // load count to data
+    @LOOP // sel main loop
+    D;JEQ // jump to main if done
+
+    // set word to 0 (white)
+    @pointer // sel pointer
+    A=M // set address to pointer value
+    M=0 // set screen word to white
+
+    // inc pointer
+    @pointer // sel pointer
+    M=M+1 // inc pointer
+
+    // dec count
+    @count // sel count
+    M=M-1 // dec count
+
+    // jump back to white loop
+    @WHITE_LOOP // sel white loop
+    0;JMP // jump back to loop