diff --git a/HISTORY.txt b/HISTORY.txt
index 51f4977..a20125d 100644
--- a/HISTORY.txt
+++ b/HISTORY.txt
@@ -27,7 +27,6 @@ of samples per frame and keeping PSG & FM chips in sync.
 * added support for 2-Cell vertical scrolling in Interlaced 2 mode
 * added proper HV Counter latch support (fixes Sunset Riders intro)
 * fixed left-most column vertical scrolling when horizontally scrolled (Gynoug, F1) 
-* fixed VBLANK transition line checks
 * improved VDP FIFO timings accuracy: fixes Sol Deace intro
 * improved sprite masking accuracy (thanks to Nemesis for his sprite test program)
 * improved HBLANK flag timing accuracy: fixes Mega Turrican (Sky level)
@@ -41,6 +40,7 @@ of samples per frame and keeping PSG & FM chips in sync.
 ---------------
 * updated Z80 core to last version (fixes interrupt Mode 0 timing and some BIT instructions).
 * fixed some Z80 instructions timing.
+* improved Z80 interrupt accuracy
 * improved 68k accuracy (initial Reset timing + auto-vectored interrupts handling).
 * improved 68k timing accuracy for DIVU/DVIS (thanks to Jorge Cwik) & MULU/MULS instructions.
 * improved Z80 & 68k cpu execution/synchronization accuracy by using Master Clock as common reference (now run exactly 3420 M-Cycles per line).
diff --git a/source/genesis.c b/source/genesis.c
index 602e91c..103de9a 100644
--- a/source/genesis.c
+++ b/source/genesis.c
@@ -125,12 +125,14 @@ void gen_hardreset(void)
   if (config.bios_enabled == 3)
     m68k_memory_map[0].base = bios_rom;
 
-  /* Reset CPU cycle counts */
-  mcycles_68k = 0;
-  mcycles_z80 = 0;
+  /* Reset CPU cycles (check EA logo corruption, no glitches for Skitchin/Budokan on PAL 60hz MD2 with TMSS) */
+  mcycles_68k = mcycles_z80 = (rand() % lines_per_frame) * MCYCLES_PER_LINE;
 
-  zstate  = 0;  /* Z80 is resetted & has control of the bus */
-  zbank   = 0;  /* Assume default bank is $000000-$007FFF */
+  /* Z80 bus is released & Z80 reset is asserted */
+  zstate = 0;
+
+  /* Assume default bank is $000000-$007FFF */
+  zbank = 0;  
 
   /* Reset 68k, Z80 & YM2612 */
   m68k_pulse_reset();
@@ -149,11 +151,11 @@ void gen_softreset(int state)
   }
   else
   {
-    /* Reset Action Replay */
+    /* Reset Pro Action Replay (required in Trainer mode) */
     if (config.lock_on == TYPE_AR)
       datel_reset(0);
 
-    /* VDP is not reseted so 68k & Z80 could restart anywhere in the emulated frame */
+    /* 68k & Z80 could restart anywhere in VDP frame (fixes Eternal Champions, X-Men 2) */
     mcycles_68k = mcycles_z80 = (uint32)((MCYCLES_PER_LINE * lines_per_frame) * ((double)rand() / (double)RAND_MAX));
 
     /* Reset 68k, Z80 & YM2612 */
@@ -199,7 +201,7 @@ void gen_reset_w(uint32 state, uint32 cycles)
   if (state == (zstate & 1))
     return;
 
-  if (state)  /* !ZRESET released */
+  if (state)  /* !ZRESET inactive */
   {
     /* if z80 is restarted, resynchronize with 68k */
     if (zstate == 0)
@@ -208,16 +210,16 @@ void gen_reset_w(uint32 state, uint32 cycles)
     /* reset Z80 */
     z80_reset();
 
-    /* release Z80 reset */
+    /* negate Z80 reset */
     zstate |= 1;
   }
-  else  /* !ZRESET enabled */
+  else  /* !ZRESET active */
   {
     /* if z80 was running, resynchronize with 68k */
     if (zstate == 1)
       z80_run(cycles);
 
-    /* hold Z80 reset */
+    /* assert Z80 reset */
     zstate &= 2;
   }
 
@@ -232,7 +234,5 @@ void gen_bank_w (uint32 state)
 
 int z80_irq_callback (int param)
 {
-  zirq = 0;
-  z80_set_irq_line (0, CLEAR_LINE);
   return 0xFF;
 }
diff --git a/source/gx/config.c b/source/gx/config.c
index 8f144ae..172ba64 100644
--- a/source/gx/config.c
+++ b/source/gx/config.c
@@ -96,7 +96,7 @@ void config_default(void)
   config.xscale   = 0;
   config.yscale   = 0;
   config.aspect   = 1;
-  config.overscan = 1;
+  config.overscan = 3;
   if (VIDEO_HaveComponentCable())
     config.render = 2;
   else
diff --git a/source/gx/fileio/file_slot.c b/source/gx/fileio/file_slot.c
index 84c03fe..2aed03a 100644
--- a/source/gx/fileio/file_slot.c
+++ b/source/gx/fileio/file_slot.c
@@ -437,7 +437,7 @@ int slot_save(int slot, int device)
       return 0;
     }
 
-    /* Read into buffer (2k blocks) */
+    /* Write from buffer (2k blocks) */
     while (filesize > FATCHUNK)
     {
       fwrite(savebuffer + done, FATCHUNK, 1, fp);
diff --git a/source/gx/gui/menu.c b/source/gx/gui/menu.c
index 262c460..fefc07b 100644
--- a/source/gx/gui/menu.c
+++ b/source/gx/gui/menu.c
@@ -1050,7 +1050,7 @@ static void systemmenu ()
         else if (config.region_detect == 2)
           sprintf (items[0].text, "Console Region:  EUR");
         else if (config.region_detect == 3)
-          sprintf (items[0].text, "Console Region:  JAP");
+          sprintf (items[0].text, "Console Region:  JPN");
 
         if (cart.romsize)
         {
@@ -1211,7 +1211,14 @@ static void videomenu ()
   else
     sprintf (items[VI_OFFSET].text, "NTSC Filter: OFF");
 
-  sprintf (items[VI_OFFSET+1].text, "Borders: %s", config.overscan ? "ON" : "OFF");
+  if (config.overscan == 3)
+    sprintf (items[VI_OFFSET+1].text, "Borders: ALL");
+  else if (config.overscan == 2)
+    sprintf (items[VI_OFFSET+1].text, "Borders: H ONLY");
+  else if (config.overscan == 1)
+    sprintf (items[VI_OFFSET+1].text, "Borders: V ONLY");
+  else
+    sprintf (items[VI_OFFSET+1].text, "Borders: NONE");
 
   if (config.aspect == 1)
     sprintf (items[VI_OFFSET+2].text,"Aspect: ORIGINAL (4:3)");
@@ -1360,8 +1367,15 @@ static void videomenu ()
         break;
 
       case VI_OFFSET+1: /*** overscan emulation ***/
-        config.overscan ^= 1;
-        sprintf (items[VI_OFFSET+1].text, "Borders: %s", config.overscan ? "ON" : "OFF");
+        config.overscan = (config.overscan + 1) % 4;
+        if (config.overscan == 3)
+          sprintf (items[VI_OFFSET+1].text, "Borders: ALL");
+        else if (config.overscan == 2)
+          sprintf (items[VI_OFFSET+1].text, "Borders: H ONLY");
+        else if (config.overscan == 1)
+          sprintf (items[VI_OFFSET+1].text, "Borders: V ONLY");
+        else
+          sprintf (items[VI_OFFSET+1].text, "Borders: NONE");
         break;
 
       case VI_OFFSET+2: /*** aspect ratio ***/
diff --git a/source/gx/gx_video.c b/source/gx/gx_video.c
index d8c5f9a..5e40a0f 100644
--- a/source/gx/gx_video.c
+++ b/source/gx/gx_video.c
@@ -1332,24 +1332,8 @@ void gx_video_Start(void)
     tvmodes[2]->xfbMode = VI_XFBMODE_DF;
   }
 
-  /* overscan emulation */
-  if (config.overscan)
-  {
-    bitmap.viewport.x = (reg[12] & 1) ? 16 : 12;
-    bitmap.viewport.y = (reg[1] & 8) ? 0 : 8;
-    if (vdp_pal)
-      bitmap.viewport.y  += 24;
-  }
-  else
-  {
-    bitmap.viewport.x = 0;
-    bitmap.viewport.y = 0;
-  }
-
-  /* reinitialize video size */
-  vwidth  = bitmap.viewport.w + (2 * bitmap.viewport.x);
-  vheight = bitmap.viewport.h + (2 * bitmap.viewport.y);
-  bitmap.viewport.changed = 1;
+  /* force video update */
+  bitmap.viewport.changed = 3;
 
   /* NTSC filter */
   if (config.ntsc)
@@ -1394,28 +1378,22 @@ void gx_video_Start(void)
 /* GX render update */
 void gx_video_Update(void)
 {
-  int update = bitmap.viewport.changed;
+  int update = bitmap.viewport.changed & 1;
 
   /* check if display has changed */
   if (update)
   {
     /* update texture size */
-    int old_vwidth = vwidth;
     vwidth = bitmap.viewport.w + (2 * bitmap.viewport.x);
     vheight = bitmap.viewport.h + (2 * bitmap.viewport.y);
 
-    /* if width has been changed, do no render this frame           */
-    /* this fixes texture glitches when changing width middle-frame */
-    if (vwidth != old_vwidth)
-      return;
-
     /* interlaced mode */
     if (config.render && interlaced)
       vheight = vheight << 1;
 
     /* ntsc filter */
     if (config.ntsc)
-      vwidth = (reg[12]&1) ? MD_NTSC_OUT_WIDTH(vwidth) : SMS_NTSC_OUT_WIDTH(vwidth);
+      vwidth = (reg[12] & 1) ? MD_NTSC_OUT_WIDTH(vwidth) : SMS_NTSC_OUT_WIDTH(vwidth);
 
     /* texels size must be multiple of 4 */
     vwidth  = (vwidth  >> 2) << 2;
@@ -1488,7 +1466,7 @@ void gx_video_Update(void)
     /* force audio DMA resynchronization */
     audioStarted = 0;
 
-    bitmap.viewport.changed = 0;
+    bitmap.viewport.changed &= ~1;
   }
 }
 
diff --git a/source/render.c b/source/render.c
index 8bb5160..c17b851 100644
--- a/source/render.c
+++ b/source/render.c
@@ -1490,8 +1490,9 @@ static void render_obj(int line, uint8 *buf, uint8 *table)
   int height;
   int v_line;
   int column;
+  int max = bitmap.viewport.w;
   int left = 0x80;
-  int right = 0x80 + bitmap.viewport.w;
+  int right = 0x80 + max;
 
   uint8 *s, *lb;
   uint16 name, index;
@@ -1506,7 +1507,9 @@ static void render_obj(int line, uint8 *buf, uint8 *table)
 
     /* sprite masking (requires at least one sprite with xpos > 0) */
     if (xpos)
+    {
       spr_over = 1;
+    }
     else if (spr_over)
     {
       spr_over = 0;
@@ -1539,9 +1542,9 @@ static void render_obj(int line, uint8 *buf, uint8 *table)
 
       /* number of tiles to draw */
       /* adjusted for sprite limit */
-      if (pixelcount > bitmap.viewport.w)
+      if (pixelcount > max)
       {
-        width -= (pixelcount - bitmap.viewport.w);
+        width -= (pixelcount - max);
       }
 
       width >>= 3;
@@ -1555,7 +1558,7 @@ static void render_obj(int line, uint8 *buf, uint8 *table)
     }
 
     /* sprite limit (256 or 320 pixels) */
-    if (pixelcount >= bitmap.viewport.w)
+    if (pixelcount >= max)
     {
       spr_over = 1;
       return;
@@ -1580,8 +1583,9 @@ static void render_obj_im2(int line, int odd, uint8 *buf, uint8 *table)
   int height;
   int v_line;
   int column;
+  int max = bitmap.viewport.w;
   int left = 0x80;
-  int right = 0x80 + bitmap.viewport.w;
+  int right = 0x80 + max;
 
   uint8 *s, *lb;
   uint16 name, index;
@@ -1597,7 +1601,9 @@ static void render_obj_im2(int line, int odd, uint8 *buf, uint8 *table)
 
     /* sprite masking (requires at least one sprite with xpos > 0) */
     if (xpos)
+    {
       spr_over = 1;
+    }
     else if(spr_over)
     {
       spr_over = 0;
@@ -1630,8 +1636,8 @@ static void render_obj_im2(int line, int odd, uint8 *buf, uint8 *table)
 
       /* number of tiles to draw */
       /* adjusted for sprite limit */
-      if (pixelcount > bitmap.viewport.w)
-        width -= (pixelcount - bitmap.viewport.w);
+      if (pixelcount > max)
+        width -= (pixelcount - max);
       width >>= 3;
 
       for(column = 0; column < width; column += 1, lb+=8)
@@ -1646,7 +1652,7 @@ static void render_obj_im2(int line, int odd, uint8 *buf, uint8 *table)
     }
 
     /* sprite limit (256 or 320 pixels) */
-    if (pixelcount >= bitmap.viewport.w)
+    if (pixelcount >= max)
     {
       spr_over = 1;
       return;
@@ -1736,25 +1742,24 @@ void render_shutdown(void)
 /* Line render function                                                     */
 /*--------------------------------------------------------------------------*/
 
-void render_line(int line, int overscan)
+void render_line(int line)
 {
-  int width    = bitmap.viewport.w;
-  int x_offset = bitmap.viewport.x;
-
   /* display OFF */
   if (reg[0] & 0x01)
     return;
 
+  uint8 *lb     = tmp_buf;
+  int width     = bitmap.viewport.w;
+  int x_offset  = bitmap.viewport.x;
+
   /* background color (blanked display or vertical borders) */
-  if (!(reg[1] & 0x40) || overscan)
+  if (!(reg[1] & 0x40) || (status & 8))
   {
     width += 2 * x_offset;
-    memset(&tmp_buf[0x20 - x_offset], 0x40, width);
+    memset(&lb[0x20 - x_offset], 0x40, width);
   }
   else
   {
-    uint8 *lb = tmp_buf;
-
     /* update pattern generator */
     if (bg_list_index)
     {
@@ -1810,7 +1815,11 @@ void render_line(int line, int overscan)
       }
     }
 
-    /* borders */
+    /* left-most column blanking */
+    if(reg[0] & 0x20)
+      memset(&lb[0x20], 0x40, 0x08);
+
+    /* horizontal borders */
     if (x_offset)
     {
         memset(&lb[0x20 - x_offset], 0x40, x_offset);
@@ -1877,7 +1886,7 @@ void window_clip(void)
   int hf = (reg[17] >> 7) & 1;
 
   /* Display size  */
-  int sw =  bitmap.viewport.w >> 4;
+  int sw = (reg[12] & 1) ? 20 : 16;
 
   /* Clear clipping data */
   memset(&clip, 0, sizeof(clip));
diff --git a/source/render.h b/source/render.h
index a4c51f5..2b9442f 100644
--- a/source/render.h
+++ b/source/render.h
@@ -31,7 +31,7 @@ extern uint32 object_index_count;
 extern void render_init(void);
 extern void render_reset(void);
 extern void render_shutdown(void);
-extern void render_line(int line, int overscan);
+extern void render_line(int line);
 extern void remap_buffer(int line,int width);
 extern void window_clip(void);
 extern void parse_satb(int line);
diff --git a/source/system.c b/source/system.c
index aa0ac1d..37e2b98 100644
--- a/source/system.c
+++ b/source/system.c
@@ -327,19 +327,52 @@ void system_shutdown (void)
  ****************************************************************/
 void system_frame (int do_skip)
 {
-  /* update display settings */
-  int line;
-  int vdp_height  = bitmap.viewport.h;
-  int end_line    = vdp_height + bitmap.viewport.y;
-  int start_line  = lines_per_frame - bitmap.viewport.y;
-  int old_interlaced = interlaced;
-  interlaced = (reg[12] & 2) >> 1;
-  if (old_interlaced != interlaced)
+  int start   = 0;
+  int end     = 0;
+  int line    = 0;
+
+  /* display changed during VBLANK */
+  if (bitmap.viewport.changed & 2)
   {
-    bitmap.viewport.changed = 1;
-    im2_flag = ((reg[12] & 6) == 6);
-    odd_frame = 1;
+    bitmap.viewport.changed &= ~2;
+
+    /* interlaced mode */
+    int old_interlaced  = interlaced;
+    interlaced = (reg[12] & 2) >> 1;
+    if (old_interlaced != interlaced)
+    {
+      im2_flag = ((reg[12] & 6) == 6);
+      odd_frame = 1;
+      bitmap.viewport.changed = 1;
+    }
+
+    /* screen height */
+    if (reg[1] & 8)
+    { 
+      bitmap.viewport.h = 240;
+      bitmap.viewport.y = (config.overscan & 1) ? (vdp_pal ? 24 : 0) : 0;
+    }
+    else
+    {
+      bitmap.viewport.h = 224;
+      bitmap.viewport.y = (config.overscan & 1) ? (vdp_pal ? 32 : 8) : 0;
+    }
+
+    /* screen width */
+    if (reg[12] & 1)
+    {
+      bitmap.viewport.w = 320;
+      bitmap.viewport.x = (config.overscan & 2) ? 16 : 0;
+    }
+    else
+    {
+      bitmap.viewport.w = 256;
+      bitmap.viewport.x = (config.overscan & 2) ? 12 : 0;
+    }
   }
+
+  /* Z80 interrupt flag */
+  int zirq = 0;
   
   /* clear VBLANK, DMA, FIFO FULL & field flags */
   status &= 0xFEE5;
@@ -349,8 +382,8 @@ void system_frame (int do_skip)
 
   /* even/odd field flag (interlaced modes only) */
   odd_frame ^= 1;
-  if (odd_frame && interlaced)
-    status |= 0x0010;
+  if (interlaced)
+    status |= (odd_frame << 4);
 
   /* reload HCounter */
   int h_counter = reg[10];
@@ -382,10 +415,10 @@ void system_frame (int do_skip)
     if (status & 8)
     {
       /* render overscan */
-      if (!do_skip && ((line < end_line) || (line >= start_line)))
-        render_line(line, 1);
+      if (!do_skip && ((line < end) || (line >= start)))
+        render_line(line);
 
-      /* clear any pending Z80 interrupt */
+      /* clear pending Z80 interrupt */
       if (zirq)
       {
         zirq = 0;
@@ -406,18 +439,34 @@ void system_frame (int do_skip)
       }
 
       /* end of active display */
-      if (line == vdp_height)
+      if (line == bitmap.viewport.h)
       {
-        /* render overscan */
-        if (!do_skip && (line < end_line))
-          render_line(line, 1);
+        /* set border area */
+        start = lines_per_frame - bitmap.viewport.y;
+        end   = bitmap.viewport.h + bitmap.viewport.y;
 
-        /* update inputs (doing this here fix Warriors of Eternal Sun) */
-        osd_input_Update();
+        /* check viewport changes */
+        if (bitmap.viewport.h != bitmap.viewport.oh)
+        {
+          bitmap.viewport.oh = bitmap.viewport.h;
+          bitmap.viewport.changed |= 1;
+        }
+        if (bitmap.viewport.w != bitmap.viewport.ow)
+        {
+          bitmap.viewport.ow = bitmap.viewport.w;
+          bitmap.viewport.changed |= 1;
+        }
 
         /* set VBLANK flag */
         status |= 0x08;
 
+        /* render overscan */
+        if (!do_skip && bitmap.viewport.y)
+          render_line(line);
+
+        /* update inputs (doing this here fix Warriors of Eternal Sun) */
+        osd_input_Update();
+
         /* Z80 interrupt is 16ms period (one frame) and 64us length (one scanline) */
         zirq = 1;
         z80_set_irq_line(0, ASSERT_LINE);
@@ -445,7 +494,7 @@ void system_frame (int do_skip)
           parse_satb(0x80 + line);
 
         /* render scanline */
-        render_line(line, 0);
+        render_line(line);
       }
     }
 
diff --git a/source/vdp.c b/source/vdp.c
index 614995b..6f4a55b 100644
--- a/source/vdp.c
+++ b/source/vdp.c
@@ -50,7 +50,6 @@ uint16 status;        /* VDP status flags */
 uint8 dmafill;        /* next VDP Write is DMA Fill */
 uint8 hint_pending;   /* 0= Line interrupt is pending */
 uint8 vint_pending;   /* 1= Frame interrupt is pending */
-uint8 zirq;           /* Z80 IRQ status */
 uint8 irq_status;     /* 68K IRQ status */
 
 /* Global variables */
@@ -161,7 +160,6 @@ void vdp_reset(void)
   pending         = 0;
   hint_pending    = 0;
   vint_pending    = 0;
-  zirq            = 0;
   irq_status      = 0;
   hvc_latch       = 0;
   v_counter       = 0;
@@ -204,21 +202,21 @@ void vdp_reset(void)
   hctab = cycle2hc32;
 
   /* reset display area */
-  bitmap.viewport.w = 256;
-  bitmap.viewport.h = 224;
-  bitmap.viewport.changed = 1;
+  bitmap.viewport.w   = 256;
+  bitmap.viewport.h   = 224;
+  bitmap.viewport.ow  = 256;
+  bitmap.viewport.oh  = 224;
 
   /* reset overscan area */
   bitmap.viewport.x = 0;
   bitmap.viewport.y = 0;
-  if (config.overscan)
-  {
-    bitmap.viewport.x = 12;
+  if (config.overscan & 1)
     bitmap.viewport.y = vdp_pal ? 32 : 8;
-  }
+  if (config.overscan & 2)
+    bitmap.viewport.x = 12;
 
-  /* initialize some registers (normally set by BIOS) */
-  if (config.bios_enabled != 3)
+  /* reset some registers normally set by BIOS */
+  if (config.bios_enabled == 1)
   {
     reg_w(0 , 0x04);  /* Palette bit set */
     reg_w(1 , 0x04);  /* Mode 5 enabled */
@@ -244,11 +242,6 @@ void vdp_restore(uint8 *vdp_regs)
   vctab = (vdp_pal) ? ((reg[1] & 8) ? vc_pal_240 : vc_pal_224) : vc_ntsc_224;
   hctab = (reg[12] & 1) ? cycle2hc40 : cycle2hc32;
 
-  /* reinitialize overscan area */
-  bitmap.viewport.x = config.overscan ? ((reg[12] & 1) ? 16 : 12) : 0;
-  bitmap.viewport.y = config.overscan ? (((reg[1] & 8) ? 0 : 8) + (vdp_pal ? 24 : 0)) : 0;
-  bitmap.viewport.changed = 1;
-
   /* restore FIFO timings */
   fifo_latency = (reg[12] & 1) ? 190 : 214;
   if ((code & 0x0F) == 0x01) 
@@ -501,18 +494,12 @@ void vdp_data_w(unsigned int data)
     /* update VDP FIFO */
     fifo_update(mcycles_68k);
 
-    if (fifo_write_cnt == 0)
-    {
-      /* reset cycle counter */
-      fifo_lastwrite = mcycles_68k;
-
-      /* FIFO is not empty anymore */
-      status &= 0xFDFF;
-    }
-
     /* increase FIFO word count */
     fifo_write_cnt ++;
 
+    /* FIFO is not empty anymore */
+    status &= 0xFDFF;
+
     /* FIFO full ? */
     if (fifo_write_cnt >= 4)
     {
@@ -818,26 +805,29 @@ static void reg_w(unsigned int r, unsigned int d)
       /* See if the viewport height has actually been changed */
       if (r & 0x08)
       {
-        /* PAL mode only ! */
+        /* Update V Counter table */
         if (vdp_pal)
+          vctab = (d & 8) ? vc_pal_240 : vc_pal_224;
+  
+        /* Update viewport */
+        if (status & 8)
         {
+          /* changes should be applied on next frame */
+          bitmap.viewport.changed |= 2;
+        }
+        else
+        {
+          /* Update active display */
           if (d & 8)
           {
             bitmap.viewport.h = 240;
-            if (config.overscan)
-              bitmap.viewport.y = 24;
-            vctab = vc_pal_240;
+            bitmap.viewport.y = (config.overscan & 1) ? (vdp_pal ? 24 : 0) : 0;
           }
           else
           {
             bitmap.viewport.h = 224;
-            if (config.overscan)
-              bitmap.viewport.y = 32;
-            vctab = vc_pal_224;
+            bitmap.viewport.y = (config.overscan & 1) ? (vdp_pal ? 32 : 8) : 0;
           }
-
-          /* update viewport */
-          bitmap.viewport.changed = 1;
         }
       }
 
@@ -861,8 +851,8 @@ static void reg_w(unsigned int r, unsigned int d)
 #ifdef LOGVDP
           error("Line redrawn (%d sprites) \n",object_index_count);
 #endif
-          /* re-render line */
-          render_line(v_counter, 0);
+          /* redraw entire line */
+          render_line(v_counter);
         }
 #ifdef LOGVDP
         else
@@ -939,12 +929,7 @@ static void reg_w(unsigned int r, unsigned int d)
 
           /* Update HC table */
           hctab = cycle2hc40;
-
-          /* Update viewport width */
-          bitmap.viewport.w = 320;
-          if (config.overscan)
-            bitmap.viewport.x = 16;
-
+            
           /* Update fifo timings */
           fifo_latency = 190;
         }
@@ -959,23 +944,50 @@ static void reg_w(unsigned int r, unsigned int d)
           /* Update HC table */
           hctab = cycle2hc32;
 
-          /* Update viewport width */
-          bitmap.viewport.w = 256;
-          if (config.overscan)
-            bitmap.viewport.x = 12;
-
           /* Update fifo timings */
           fifo_latency = 214;
         }
-		
-	    if ((code & 0x0F) == 0x01)
-		  fifo_latency *= 2;
 
-        /* Update viewport */
-        bitmap.viewport.changed = 1;
+        if ((code & 0x0F) == 0x01)
+          fifo_latency = fifo_latency * 2;
 
         /* Update clipping */
         window_clip();
+        
+        /* Update viewport */
+        if (status & 8)
+        {
+          /* changes should be applied on next frame */
+          bitmap.viewport.changed |= 2;
+        }
+        else
+        {
+          /* Update active display */
+          if (d & 1)
+          {
+            bitmap.viewport.w = 320;
+            bitmap.viewport.x = (config.overscan & 2) ? 16 : 0;
+          }
+          else
+          {
+            bitmap.viewport.w = 256;
+            bitmap.viewport.x = (config.overscan & 2) ? 12 : 0;
+          }
+
+          /* display width changed during HBLANK (Bugs Bunny Double Trouble) */
+          if (mcycles_68k <= (mcycles_vdp + 860))
+          {
+            /* redraw entire line */
+            render_line(v_counter);
+          }
+        }
+      }
+
+      /* Interlaced modes */
+      if (r & 0x06)
+      {
+        /* changes should be applied on next frame */
+        bitmap.viewport.changed |= 2;
       }
 
       /* See if the S/TE mode bit has changed */
diff --git a/source/vdp.h b/source/vdp.h
index 5ebecdd..bc980ed 100644
--- a/source/vdp.h
+++ b/source/vdp.h
@@ -38,7 +38,6 @@ extern uint16 status;
 extern uint8 dmafill;
 extern uint8 hint_pending;
 extern uint8 vint_pending;
-extern uint8 zirq;
 extern uint8 irq_status;
 
 /* Global variables */