diff --git a/assembler.c b/assembler.c
index 6623056..140a941 100644
--- a/assembler.c
+++ b/assembler.c
@@ -140,6 +140,8 @@ makevariable(char *id, Uint16 *addr, FILE *f)
 	char wv[64];
 	Uint8 origin;
 	fscanf(f, "%s", wv);
+	if(!sihx(wv))
+		return error("Variable value is invalid", wv);
 	origin = *addr;
 	*addr += shex(wv);
 	return makelabel(id, origin, shex(wv));
diff --git a/build.sh b/build.sh
index 764d44b..0c71945 100755
--- a/build.sh
+++ b/build.sh
@@ -19,5 +19,5 @@ rm -f ./bin/emulator
 cc -std=c89 -DDEBUG -Wall -Wno-unknown-pragmas -Wpedantic -Wshadow -Wextra -Werror=implicit-int -Werror=incompatible-pointer-types -Werror=int-conversion -Wvla -g -Og -fsanitize=address -fsanitize=undefined uxn.c emulator.c -L/usr/local/lib -lSDL2 -o bin/emulator
 
 # run
-./bin/assembler examples/controller.usm bin/boot.rom
+./bin/assembler examples/drag.usm bin/boot.rom
 ./bin/emulator bin/boot.rom
diff --git a/emulator.c b/emulator.c
index f2fc7d4..fa153ae 100644
--- a/emulator.c
+++ b/emulator.c
@@ -252,8 +252,10 @@ screenw(Device *d, Memory *m, Uint8 b)
 			(d->mem[2] << 8) + d->mem[3],
 			(d->mem[0] << 8) + d->mem[1],
 			d->mem[4]);
-		if(d->mem[5])
+		if(d->mem[5] == 1)
 			REQDRAW = 1;
+		if(d->mem[5] == 2)
+			clear(pixels);
 		d->ptr = 0;
 	}
 	(void)m;
diff --git a/examples/controller.usm b/examples/controller.usm
index f7af7d2..8f5337d 100644
--- a/examples/controller.usm
+++ b/examples/controller.usm
@@ -1,4 +1,4 @@
-( comment )
+( controller )
 
 :dev/r fff8 ( const read port )
 :dev/w fff9 ( const write port )
diff --git a/examples/drag.usm b/examples/drag.usm
new file mode 100644
index 0000000..d3867b7
--- /dev/null
+++ b/examples/drag.usm
@@ -0,0 +1,69 @@
+( drag )
+
+:dev/r fff8 ( std read port )
+:dev/w fff9 ( std write port )
+
+;drawx 2 ;drawy 2 ;x 2 ;y 2 ;w 2 ;h 2 ;color 1
+
+|0100 @RESET 
+	
+	#05 =dev/r ( set dev/read mouse )
+	#01 =dev/w ( set dev/write to screen ) 
+
+BRK
+
+|c000 @FRAME
+	
+	( get touch )
+	#04 IOR #01 NEQ ,frame-end ROT JMP? POP2
+
+	( clear )
+	#00 =color
+	~x ~y #0060 #0040 ,fillrect JSR
+
+	( fill rect x y w h )
+	#01 =color
+	#00 IOR2 ( get mouse-x ) =x
+	#02 IOR2 ( get mouse-y ) =y
+	~x ~y #0060 #0040 ,fillrect JSR
+	
+	,redraw JSR
+
+	@frame-end
+
+BRK
+
+@fillrect
+	=h =w =y =x ( store values in variables )
+	~x =drawx ~y =drawy ( store draw pos in variables )
+	@fillrectrow
+		~x =drawx
+		@fillrectcol
+			( draw ) ~drawx ~drawy IOW2 IOW2 ~color IOW  #00 IOW
+			~drawx #0001 ADD2 =drawx 
+			~drawx ~w ~x ADD2 LTH2 ,fillrectcol ROT JMP? POP2
+		~drawy #0001 ADD2 =drawy 
+		~drawy ~h ~y ADD2 LTH2 ,fillrectrow ROT JMP? POP2
+	RTS
+
+@getmouse
+	#00 IOR2 ( get mouse x )
+	#02 IOR2 ( get mouse y )
+	RTS
+
+@redraw
+	#0000 IOW2
+	#0000 IOW2
+	#00 IOW
+	#01 IOW
+	RTS
+
+@clear
+	#0000 IOW2
+	#0000 IOW2
+	#00 IOW
+	#02 IOW
+	RTS
+
+|d000 @ERROR BRK 
+|FFFA .RESET .FRAME .ERROR
diff --git a/examples/hello.usm b/examples/hello.usm
index de9e9f5..7deb656 100644
--- a/examples/hello.usm
+++ b/examples/hello.usm
@@ -1,4 +1,4 @@
-( comment )
+( hello world )
 
 :dev/w fff9 ( const write port )
 
@@ -32,11 +32,11 @@ BRK
 
 @displaygui
 	#02 =dev/w                                   ( set dev/write to sprite ) 
-	@displayguiloop
+	@guiloop
 		DUP2 LDR ,printchar JSR
 		#0001 ADD2
 		~x #0008 ADD2 =x
-		DUP2 LDR #00 NEQ ,displayguiloop ROT JMP? POP2
+		DUP2 LDR #00 NEQ ,guiloop ROT JMP? POP2
 	RTS
 
 @printchar
diff --git a/examples/pixels.usm b/examples/pixels.usm
index 87223e0..0d46b52 100644
--- a/examples/pixels.usm
+++ b/examples/pixels.usm
@@ -1,4 +1,4 @@
-( my default test file )
+( pixels )
 
 :dev/r fff8 ( std read port )
 :dev/w fff9 ( std write port )
diff --git a/examples/sprite.usm b/examples/sprite.usm
index 66abdfd..2497e11 100644
--- a/examples/sprite.usm
+++ b/examples/sprite.usm
@@ -1,4 +1,4 @@
-( comment )
+( sprite )
 
 :dev/w fff9 ( const write port )