diff --git a/z80.cpp b/z80.cpp
index f628464..db9aa87 100644
--- a/z80.cpp
+++ b/z80.cpp
@@ -1153,8 +1153,9 @@ namespace z80
             const uint8_t opcode = READ_M1();
 
             uint8_t tag = z80mem::get()->getTag(current_opcode_address);
-            if ( !(tag & MEMTAG_IGNORE) ) tag = tag | MEMTAG_INST;
-            z80mem::get()->setTag(current_opcode_address, tag | !(tag&MEMTAG_TOUCHED) ? MEMTAG_TREPEAT : MEMTAG_TINST);
+            if ( !(tag & MEMTAG_IGNORE) )
+                tag = tag | MEMTAG_INST;
+            z80mem::get()->setTag(current_opcode_address, tag | (!(tag&MEMTAG_TOUCHED) ? MEMTAG_TREPEAT : MEMTAG_TINST) );
 
             uint16_t tmp;
             
diff --git a/z80debug.cpp b/z80debug.cpp
index 8d4d1b4..bef20da 100644
--- a/z80debug.cpp
+++ b/z80debug.cpp
@@ -1041,6 +1041,7 @@ namespace z80debug
 
     void setcursor(const uint16_t address)
     {
+        //if (!debugging()) return;
         if ( !(z80mem::get()->getTag(address) & MEMTAG_INST) )
             cursor = find_previous_opcode(address);
         else
diff --git a/z80mem.cpp b/z80mem.cpp
new file mode 100644
index 0000000..6989d5f
--- /dev/null
+++ b/z80mem.cpp
@@ -0,0 +1,3 @@
+#include "z80mem.h"
+
+z80mem* z80mem::singleton= nullptr;
diff --git a/z80mem.h b/z80mem.h
index abac0ff..b1a50c6 100644
--- a/z80mem.h
+++ b/z80mem.h
@@ -21,19 +21,19 @@ class z80mem
     public:
         static z80mem *get() { return singleton; };
 
-        virtual uint8_t readMem(uint16_t address);
-        virtual void writeMem(uint16_t address, uint8_t value);
+        virtual uint8_t readMem(uint16_t address) = 0;
+        virtual void writeMem(uint16_t address, uint8_t value) = 0;
 
-        virtual void loadMem(uint16_t address, uint16_t len, uint8_t *buffer);
+        virtual void loadMem(uint16_t address, uint16_t len, uint8_t *buffer) = 0;
 
-        virtual uint8_t getTag(uint16_t address);
-        virtual void setTag(uint16_t address, uint8_t value);
-        virtual void reset();
+        virtual uint8_t getTag(uint16_t address) = 0;
+        virtual void setTag(uint16_t address, uint8_t value) = 0;
+        virtual void reset() = 0;
 
-        virtual void saveState(FILE* f);
-        virtual void loadState(FILE* f);
+        virtual void saveState(FILE* f) = 0;
+        virtual void loadState(FILE* f) = 0;
 
-        virtual uint32_t getSize();
+        virtual uint32_t getSize() = 0;
     
     protected:
 
diff --git a/zx_48mem.h b/zx_48mem.h
index cb03ad8..b1fa26f 100644
--- a/zx_48mem.h
+++ b/zx_48mem.h
@@ -23,7 +23,7 @@ class zx_48mem : public z80mem
     
     protected:
 
-        static uint8_t memory[65536];
-        static uint8_t tags[65536];
+        uint8_t memory[65536];
+        uint8_t tags[65536];
 
 };
diff --git a/zx_screen.cpp b/zx_screen.cpp
index 00bb65a..7b47ac4 100644
--- a/zx_screen.cpp
+++ b/zx_screen.cpp
@@ -38,6 +38,9 @@ namespace zxscreen
     uint8_t zx_pixels[352*296];
     uint8_t *ptr_pixel = zx_pixels;
 
+    #define SCREEN_SYNC     0xFFFF
+    #define SCREEN_BORDER   0xFFFE
+
     void create_tables()
     {
         uint32_t count = 0;
@@ -46,24 +49,24 @@ namespace zxscreen
         uint16_t *ptr_color = color_addr;
 
         // vsync
-        for (int i=0; i<224*16;++i) { *(ptr_pixel++) = 0; *(ptr_color++) = 0; }
+        for (int i=0; i<224*16;++i) { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_SYNC; }
 
         // Upper border
         for (int i=0; i<48;++i) {
             // hsync
-            for (int j=0;j<48;++j)  { *(ptr_pixel++) = 0; *(ptr_color++) = 0; }
+            for (int j=0;j<48;++j)  { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_SYNC; }
             //border
-            for (int j=0;j<176;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = 1; count+=2; }
+            for (int j=0;j<176;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_BORDER; count+=2; }
         }
 
         // scanlines
         for (uint8_t y=0; y<192; ++y)
         {
             // hsync
-            for (int j=0;j<48;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = 0; }
+            for (int j=0;j<48;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_SYNC; }
 
             // Left border
-            for (int j=0;j<24;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = 1; count+=2; }
+            for (int j=0;j<24;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_BORDER; count+=2; }
 
             // Actual screen
             for (uint8_t x=0;x<32;++x)
@@ -79,15 +82,15 @@ namespace zxscreen
             }
 
             // Right border
-            for (int j=0;j<24;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = 1; count+=2; }
+            for (int j=0;j<24;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_BORDER; count+=2; }
         }
 
         // Lower border
         for (int i=0; i<56;++i) {
             // hsync
-            for (int j=0;j<48;++j)  { *(ptr_pixel++) = 0; *(ptr_color++) = 0; }
+            for (int j=0;j<48;++j)  { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_SYNC; }
             //border
-            for (int j=0;j<176;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = 1; count+=2; }
+            for (int j=0;j<176;++j) { *(ptr_pixel++) = 0; *(ptr_color++) = SCREEN_BORDER; count+=2; }
         }
         //printf("COUNT: %i\n", count);
     }
@@ -194,9 +197,9 @@ namespace zxscreen
 
         for (int i=0;i<dt;++i)
         {
-            if (color_addr[t_screen] != 0)
+            if (color_addr[t_screen] != SCREEN_SYNC)
             {
-                if (color_addr[t_screen] == 1) {
+                if (color_addr[t_screen] == SCREEN_BORDER) {
                     *(ptr_pixel++) = border_color;
                     *(ptr_pixel++) = border_color;
                 } else {