diff --git a/src/main.c b/src/main.c
index 8903eed..b870fab 100644
--- a/src/main.c
+++ b/src/main.c
@@ -17,9 +17,9 @@ int main(int argc, char *argv[])
 
   ScreenInit(800,400);
   VCPUInit();
-  //  MemDump();
+  //MemDump();
   int i=0;
-  
+
   while (!WindowShouldClose()){
     VCPUFetch();
     VCPUDecode();
diff --git a/src/mem.c b/src/mem.c
index 12b039f..ec34750 100644
--- a/src/mem.c
+++ b/src/mem.c
@@ -7,7 +7,7 @@ extern unsigned char DEFAULT_FONT[];
 
 void MemInit(){
   MemSet(0,0,4096);
-  MemCopy(DEFAULT_FONT,16*5,ADDR_FONT);
+  MemStore(DEFAULT_FONT,16*5,ADDR_FONT);
 }
 
 void MemSet(int addr, unsigned char value, int size){
@@ -15,12 +15,12 @@ void MemSet(int addr, unsigned char value, int size){
     memory[addr+i]=value;
 }
 
-void MemCopy(unsigned char *data, int size, int addr){
+void MemStore(unsigned char *data, int size, int addr){
   for(int i=0;i<size;i++)
     memory[addr+i]=data[i];
 }
 
-void MemRead(unsigned char *data, int size, int addr){
+void MemLoad(unsigned char *data, int size, int addr){
   int location=addr;
   for(int i=0;i<size;i++){
     data[i]=memory[addr+i];
@@ -33,6 +33,8 @@ void MemLoadROM(char *path){
   ptr=fopen(path,"rb");
   int location=ADDR_ROM;
   while(fread(&byte,1,1,ptr)==1){
+    if(location >= 4096)
+      break;
     MemSet(location,byte,1);
     location++;
   }
@@ -40,7 +42,11 @@ void MemLoadROM(char *path){
 }
 
 void MemDump(){
-  for(int addr=0;addr<4096;addr+=2){
+  MemDumpRange(0,4096);
+}
+
+void MemDumpRange(int from, int size){
+  for(int addr=from;addr<from+size;addr+=2){
     printf("0x%03x: %02x %02x\n",addr,memory[addr], memory[addr+1]);
   }
 }
diff --git a/src/mem.h b/src/mem.h
index 3f5eb95..8e4136a 100644
--- a/src/mem.h
+++ b/src/mem.h
@@ -5,7 +5,8 @@
 
 void MemInit();
 void MemSet(int addr, unsigned char value, int size);
-void MemCopy(unsigned char *data, int size, int addr);
-void MemRead(unsigned char *data, int size, int addr);
+void MemStore(unsigned char *data, int size, int addr);
+void MemLoad(unsigned char *data, int size, int addr);
 void MemLoadROM(char *path);
 void MemDump();
+void MemDumpRange(int addr, int size);
diff --git a/src/screen.c b/src/screen.c
index f4eb7ae..fa4a9c4 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -41,10 +41,20 @@ void ScreenUpdate(){
 }
 
 char ScreenPixelApply(int x, int y, unsigned char state){
-  if(Screen.pixels[x+y*64] != 0 && state != 0)
-    return 1;
-  Screen.pixels[x+y*64]=state;
-  return 0;
+  char flag=0;
+  
+  // Toggle pixel if state is on
+  if(state){
+    if(Screen.pixels[x+y*64]){
+      Screen.pixels[x+y*64]=0;
+      flag=1;
+    }
+    else{
+      Screen.pixels[x+y*64]=1;
+    }
+  }
+  
+  return flag;
 }
 
 void ScreenPixelFlip(int x, int y){
diff --git a/src/vcpu.c b/src/vcpu.c
index c3e1e5e..bd255ef 100644
--- a/src/vcpu.c
+++ b/src/vcpu.c
@@ -16,7 +16,7 @@ void VCPUInit(){
 
 void VCPUFetch(){
   unsigned char byte[2];
-  MemRead(byte,2,State.PC); // Little indian to -1 no +1
+  MemLoad(byte,2,State.PC); // Little indian to -1 no +1
   State.opcode=byte[0];
   State.opcode=State.opcode<<8;
   State.opcode=State.opcode | byte[1];
@@ -56,7 +56,7 @@ void VCPUDoubleDabble(unsigned char x, unsigned char *u, unsigned char *t, unsig
 }
 
 void VCPUExecute(){
-  VCPUDump();
+  //  VCPUDump();
   switch(State.opcode >> 12){
   case 0x0: // Clear screen or return from subroutine
     if(State.N == 0x0){ // Clear screen
@@ -185,17 +185,17 @@ void VCPUExecute(){
     break;
       
   case 0xD: // Draw a sprite
-    int X=State.V[State.X]&63;
-    int Y=State.V[State.Y]&31;
     State.V[REG_FLAG]=0; // Set flag to 0
     int width, height;
     ScreenWH(&width,&height);
+    int X=State.V[State.X]%width;
+    int Y=State.V[State.Y]%height;
     for(char row=0;row<State.N;row++){
       // Stop if row out of screen
       if(Y+row>=height)
         break;
       unsigned char sprite;
-      MemRead(&sprite,1,State.I+row); // Load sprite
+      MemLoad(&sprite,1,State.I+row); // Load sprite
       // Draw sprite
       for(int shift=0;shift<8;shift++){
         // Stop if column is out of screen
@@ -240,18 +240,18 @@ void VCPUExecute(){
     case 0x33:
       unsigned char units, tens, hundreds;
       VCPUDoubleDabble(State.V[State.X],&units,&tens,&hundreds);
-      MemCopy(&hundreds,1,State.I);
-      MemCopy(&tens,1,State.I+1);
-      MemCopy(&units,1,State.I+2);
+      MemStore(&hundreds,1,State.I);
+      MemStore(&tens,1,State.I+1);
+      MemStore(&units,1,State.I+2);
       //      printf("hundreds:%d tens:%d units:%d byte:%d\n",hundreds,tens,units,State.V[State.X]);
       break;
       
     case 0x55:
-      MemCopy(State.V,0xF,State.I);
+      MemStore(State.V,16,State.I);
       break;
       
     case 0x65:
-      MemRead(State.V,0xF,State.I);
+      MemLoad(State.V,16,State.I);
       break;
       
     }
@@ -266,4 +266,7 @@ void VCPUDump(){
   printf("N: 0x%01x\n",State.N);
   printf("NN: 0x%02x\n",State.NN);
   printf("NNN: 0x%03x\n",State.NNN);
+  for(int i=0;i<16;i++){
+    printf("V%d: 0x%02x\n",i,State.V[i]);
+  }
 }