diff --git a/src/vcpu.c b/src/vcpu.c
index 80323e3..f660dc3 100644
--- a/src/vcpu.c
+++ b/src/vcpu.c
@@ -35,11 +35,11 @@ void VCPUDecode(){
 void VCPUExecute(){
   //  VCPUDump();
   switch(State.opcode >> 12){
-  case 0x0:
+  case 0x0: // Clear screen
     ScreenClear();
     break
       ;;
-  case 0x1:
+  case 0x1: // Jump
     State.PC=State.NNN;
     break
       ;;
diff --git a/src/vcpu.h b/src/vcpu.h
index bd4d2d5..dbcba0a 100644
--- a/src/vcpu.h
+++ b/src/vcpu.h
@@ -11,6 +11,7 @@ typedef struct VCPU_State {
 
   // Stack register (16 bits)
   unsigned short S;
+  unsigned short stack[100]; // Emulated stack
 
   // General purpose registers (8 bits each)
   // Note last one often used as a flag register