diff --git a/presets/atari7800/atari7800.h b/presets/atari7800/atari7800.h
index 98f35369..15c1f3b4 100644
--- a/presets/atari7800/atari7800.h
+++ b/presets/atari7800/atari7800.h
@@ -1,3 +1,5 @@
+#ifndef _ATARI7800
+#define _ATARI7800
 
 // define basic types for convenience
 typedef unsigned char byte;	// 8-bit unsigned
@@ -140,3 +142,5 @@ typedef struct DL5Entry {
 
 #define STROBE(addr)	__asm__ ("sta %w", addr)
 #define WSYNC()		STROBE(0x24)
+
+#endif
diff --git a/presets/atari7800/dlist.c b/presets/atari7800/dlist.c
deleted file mode 100644
index 42640551..00000000
--- a/presets/atari7800/dlist.c
+++ /dev/null
@@ -1,133 +0,0 @@
-
-#include "atari7800.h"
-
-#include <string.h>
-
-//#link "chr_font.s"
-
-//#link "generic8x16.s"
-
-#define SLOTHEIGHT 16
-#define DOUBLEBUFFER
-
-#ifdef DOUBLEBUFFER
-#define NUMSLOTS 32
-#define SLOTSIZE 32
-byte slot0 = 0;
-#else
-#define NUMSLOTS 16
-#define SLOTSIZE 64
-const byte slot0 = 0;
-#endif
-
-
-byte DL[NUMSLOTS][SLOTSIZE];
-byte DL_len[NUMSLOTS];
-DLLEntry DLL[NUMSLOTS];
-
-void dll_clear() {
-  byte i;
-  for (i=slot0; i<slot0+16; i++) {
-    DL[i][1] = 0;
-    DL_len[i] = 0;
-  }
-}
-
-#ifdef DOUBLEBUFFER
-void dll_swap() {
-  slot0 ^= 16;
-  if (!slot0) {
-    MARIA.DPPH = (word)(DLL+16)>>8;
-    MARIA.DPPL = (byte)(DLL+16);
-  } else {
-    MARIA.DPPH = (word)DLL>>8;
-    MARIA.DPPL = (byte)DLL;
-  }
-}
-#endif
-
-void* dll_alloc(byte slot, byte len) {
-  byte dlofs;
-  slot &= NUMSLOTS-1;
-  dlofs = DL_len[slot];
-  DL_len[slot] += len;
-  DL[slot][dlofs+len+1] = 0;
-  return &DL[slot][dlofs];
-}
-
-void dll_add_sprite(word addr, byte x, byte y, byte wpal) {
-  byte slot = (y >> 4) | slot0;
-  register DL4Entry* dl = (DL4Entry*) dll_alloc(slot, 4);
-  dl->data_lo = (byte)addr;
-  dl->data_hi = (byte)(addr>>8) + (y & 15);
-  dl->xpos = x;
-  dl->width_pal = wpal;
-  if (y & 15) {
-    DL4Entry* dl2 = (DL4Entry*) dll_alloc(slot+1, 4);
-    *dl2 = *dl;
-    dl2->data_hi -= SLOTHEIGHT;
-  }
-}
-
-void dll_add_string(const char* str, byte x, byte y, byte wpal) {
-  byte slot = (y >> 4) | slot0;
-  register DL5Entry* dl = (DL5Entry*) dll_alloc(slot, 5);
-  dl->data_lo = (byte)str;
-  dl->data_hi = (word)str>>8;
-  dl->flags = DL5_INDIRECT;
-  dl->width_pal = wpal;
-  dl->xpos = x;
-}
-
-void dll_setup() {
-  byte i;
-  byte* dlptr = &DL[0][0];
-  register DLLEntry *dll = &DLL[0];
-  for (i=0; i<NUMSLOTS; i++) {
-    dll->offset_flags = DLL_H16 | (SLOTHEIGHT-1);
-    dll->dl_hi = (word)dlptr>>8;
-    dll->dl_lo = (byte)dlptr;
-    dlptr += sizeof(DL[0]);
-    dll++;
-  }
-  dll_clear();
-#ifdef DOUBLEBUFFER
-  dll_swap();
-  dll_clear();
-#endif
-}
-
-char* hello = "\2\4\6\0\220\222\102";
-
-void main() {
-  byte i;
-  byte y = 0;
-
-  dll_setup();
-  
-  // activate DMA
-  MARIA.CHARBASE = 0x80;
-  MARIA.DPPH = (word)DLL>>8;
-  MARIA.DPPL = (byte)DLL;
-  MARIA.CTRL = CTRL_DMA_ON | CTRL_DBLBYTE | CTRL_160AB;
-  MARIA.P0C1 = 0x8f;
-  MARIA.P0C2 = 0x4f;
-  MARIA.P0C3 = 0x1f;
-  MARIA.P1C1 = 0x34;
-  MARIA.P1C2 = 0x28;
-  MARIA.P1C3 = 0x1f;
-  MARIA.BACKGRND = 0;
-
-  while (1) {
-    while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
-    dll_swap();
-    dll_clear();
-    dll_add_string(hello, y+32, 32, DL_WP(8,0));
-    for (i=0; i<8; i++) {
-      dll_add_sprite(0xa068, i*4, i*16+y, DL_WP(4,1));
-      dll_add_sprite(0xa06c, i*8+y, i*16, DL_WP(4,1));
-    }
-    while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
-    y++;
-  }
-}
diff --git a/presets/atari7800/dll.c b/presets/atari7800/dll.c
new file mode 100644
index 00000000..058ecbbd
--- /dev/null
+++ b/presets/atari7800/dll.c
@@ -0,0 +1,150 @@
+
+#include "dll.h"
+#include <string.h>
+
+DLLEntry DLL[NUMSLOTS];		// display list list
+byte DL[NUMSLOTS][SLOTSIZE];	// display list slots
+byte DL_len[NUMSLOTS];		// current bytes in each slot
+#ifdef DLSAVE
+byte DL_save[NUMSLOTS];		// save lengths of each slot
+#endif
+
+byte slot0 = 0;			// current page offset
+
+// set display list list address registers
+void dll_set_addr(const void* dpp) {
+  MARIA.DPPH = (word)dpp>>8;
+  MARIA.DPPL = (byte)dpp;
+}
+
+// clear the current page
+void dll_clear() {
+  byte i;
+  for (i=slot0; i<slot0+SLOTSPERPAGE; i++) {
+    DL_len[i] = 0;
+    DL[i][1] = 0;
+  }
+}
+
+#ifdef DLSAVE
+// save display list lengths of each slot
+void dll_save() {
+  memcpy(DL_save, DL_len, sizeof(DL_save));
+}
+
+// restore display list lengths of current page
+void dll_restore() {
+  byte i;
+  for (i=slot0; i<slot0+SLOTSPERPAGE; i++) {
+    DL_len[i] = DL_save[i]; // set slot length
+    DL[i][DL_len[i]+1] = 0; // set end marker
+  }
+}
+
+// restore all slots
+void dll_restore_all() {
+  slot0 ^= SLOTSPERPAGE;
+  dll_restore();
+  slot0 ^= SLOTSPERPAGE;
+  dll_restore();
+}
+#endif
+
+#ifdef DOUBLEBUFFER
+// swap between pages
+void dll_swap() {
+  slot0 ^= SLOTSPERPAGE;
+  if (!slot0) {
+    dll_set_addr(DLL+SLOTSPERPAGE);
+  } else {
+    dll_set_addr(DLL);
+  }
+}
+
+// copy offscreen page to current page
+void dll_copy() {
+  memcpy(&DL[slot0], &DL[slot0 ^ SLOTSPERPAGE], SLOTSIZE*SLOTSPERPAGE);
+  memcpy(&DL_len[slot0], &DL_len[slot0 ^ SLOTSPERPAGE], SLOTSPERPAGE);
+}
+#endif
+
+// set scroll position
+void dll_set_scroll(byte y) {
+  static byte oldslot = 0;
+  byte slot = y / SLOTHEIGHT;
+  byte offset = 15 - (y & 15);
+  DLL[oldslot].offset_flags = DLL_FLAGS | (SLOTHEIGHT-1);
+  DLL[slot].offset_flags = DLL_FLAGS | offset;
+  dll_set_addr(DLL + slot);
+  oldslot = slot;
+}
+
+// allocate a given # of bytes in a slot
+sbyte dll_bytesleft(byte slot) {
+  slot &= NUMSLOTS-1;
+  return SLOTSIZE - DL_len[slot];
+}
+
+// allocate a given # of bytes in a slot
+void* dll_alloc(byte slot, byte len) {
+  byte dlofs;
+  register byte* dl;
+  slot &= NUMSLOTS-1;
+  dl = DL[slot];
+  dlofs = DL_len[slot];
+  DL_len[slot] += len;
+  dl[dlofs+len+1] = 0;
+  return &dl[dlofs];
+}
+
+// add a sprite to currently selected page
+void dll_add_sprite(word addr, byte x, byte y, byte wpal) {
+  byte slot = (y / SLOTHEIGHT) | slot0;
+  register DL4Entry* dl = (DL4Entry*) dll_alloc(slot, 4);
+  dl->data_lo = (byte)addr;
+  dl->data_hi = (byte)(addr>>8) + (y & 15);
+  dl->xpos = x;
+  dl->width_pal = wpal;
+  if (y & 15) {
+    DL4Entry* dl2 = (DL4Entry*) dll_alloc(slot+1, 4);
+    *dl2 = *dl;
+    dl2->data_hi -= SLOTHEIGHT;
+  }
+}
+
+// add a string to currently selected page
+// strings are aligned to top of slot
+void dll_add_string(const char* str, byte x, byte y, byte wpal) {
+  byte slot = (y / SLOTHEIGHT) | slot0;
+  register DL5Entry* dl = (DL5Entry*) dll_alloc(slot, 5);
+  dl->data_lo = (byte)str;
+  dl->data_hi = (word)str>>8;
+  dl->flags = DL5_INDIRECT;
+  dl->width_pal = wpal;
+  dl->xpos = x;
+}
+
+// set up display lists
+void dll_setup() {
+  byte i;
+  byte* dlptr = &DL[0][0];
+  register DLLEntry *dll = &DLL[0];
+  for (i=0; i<NUMSLOTS; i++) {
+    dll->offset_flags = DLL_FLAGS | (SLOTHEIGHT-1);
+    dll->dl_hi = (word)dlptr>>8;
+    dll->dl_lo = (byte)dlptr;
+    dlptr += sizeof(DL[0]);
+    dll++;
+  }
+  dll_clear();
+#ifdef DOUBLEBUFFER
+  dll_swap();
+  dll_clear();
+  dll_swap();
+#else
+  dll_set_addr(DLL);
+#endif
+#ifdef DLSAVE
+  memset(DL_save, 0, sizeof(DL_save));
+#endif
+}
diff --git a/presets/atari7800/dll.h b/presets/atari7800/dll.h
new file mode 100644
index 00000000..5e7b4976
--- /dev/null
+++ b/presets/atari7800/dll.h
@@ -0,0 +1,46 @@
+#ifndef _DLL_H
+#define _DLL_H
+
+#include "atari7800.h"
+
+#define DLL_FLAGS DLL_H16	// 4k DMA holes
+#define SLOTHEIGHT 16		// lines per display list
+#define SLOTSIZE 32		// bytes per display list
+#define SLOTSPERPAGE 16		// display lists per page
+#define DOUBLEBUFFER		// double buffer (2 pages)
+#define DLSAVE			// enable save buffer
+
+#ifdef DOUBLEBUFFER
+#define NUMPAGES 2
+#else
+#define NUMPAGES 1
+#endif
+#define NUMSLOTS (SLOTSPERPAGE*NUMPAGES)
+
+extern DLLEntry DLL[NUMSLOTS];		// display list list
+extern byte DL[NUMSLOTS][SLOTSIZE];	// display list slots
+extern byte DL_len[NUMSLOTS];		// current bytes in each slot
+#ifdef DLSAVE
+extern byte DL_save[NUMSLOTS];		// save lengths of each slot
+#endif
+
+// set current page (0 or 1)
+#define dll_page(page) (slot0 = (page)*SLOTSPERPAGE)
+
+extern byte slot0;
+
+void dll_setup(void);
+void dll_add_string(const char* str, byte x, byte y, byte wpal);
+void dll_add_sprite(word addr, byte x, byte y, byte wpal);
+sbyte dll_bytesleft(byte slot);
+void* dll_alloc(byte slot, byte len);
+void dll_set_scroll(byte y);
+void dll_save(void);
+void dll_restore(void);
+void dll_restore_all(void);
+void dll_clear(void);
+
+void dll_swap(void);
+void dll_copy(void);
+
+#endif
diff --git a/presets/atari7800/scroll.c b/presets/atari7800/scroll.c
index 14d76f0f..8fd74df7 100644
--- a/presets/atari7800/scroll.c
+++ b/presets/atari7800/scroll.c
@@ -12,141 +12,14 @@ be written while the other is displayed.
 */
 
 #include "atari7800.h"
-
 #include <string.h>
 
+#include "dll.h"
+//#link "dll.c"
+
 //#link "chr_font.s"
 //#link "generic8x16.s"
 
-#define DLL_FLAGS DLL_H16
-#define SLOTHEIGHT 16
-#define SLOTSIZE 32
-#define DOUBLEBUFFER
-#define DLSAVE
-
-#ifdef DOUBLEBUFFER
-#define NUMSLOTS 32
-byte slot0 = 0;
-#else
-#define NUMSLOTS 16
-const byte slot0 = 0;
-#endif
-
-
-DLLEntry DLL[NUMSLOTS];
-
-byte DL[NUMSLOTS][SLOTSIZE];
-byte DL_len[NUMSLOTS];
-
-#ifdef DLSAVE
-byte DL_save[NUMSLOTS];
-#endif
-
-void dll_set_addr(const void* dpp) {
-  MARIA.DPPH = (word)dpp>>8;
-  MARIA.DPPL = (byte)dpp;
-}
-
-void dll_clear() {
-  byte i;
-  for (i=slot0; i<slot0+16; i++) {
-    DL_len[i] = 0;
-    DL[i][1] = 0;
-  }
-}
-
-#ifdef DLSAVE
-void dll_save() {
-  memcpy(DL_save, DL_len, sizeof(DL_save));
-}
-
-void dll_restore() {
-  byte i;
-  memcpy(DL_len, DL_save, sizeof(DL_save));
-  for (i=0; i<NUMSLOTS; i++) {
-    DL[i][DL_len[i]+1] = 0;
-  }
-}
-#endif
-
-#ifdef DOUBLEBUFFER
-void dll_swap() {
-  slot0 ^= 16;
-  if (!slot0) {
-    dll_set_addr(DLL+16);
-  } else {
-    dll_set_addr(DLL);
-  }
-}
-#endif
-
-void dll_set_scroll(byte y) {
-  static byte oldslot = 0;
-  byte slot = y / SLOTHEIGHT;
-  byte offset = 15 - (y & 15);
-  DLL[oldslot].offset_flags = DLL_FLAGS | (SLOTHEIGHT-1);
-  DLL[slot].offset_flags = DLL_FLAGS | offset;
-  dll_set_addr(DLL + slot);
-  oldslot = slot;
-}
-
-void* dll_alloc(byte slot, byte len) {
-  byte dlofs;
-  slot &= NUMSLOTS-1;
-  dlofs = DL_len[slot];
-  DL_len[slot] += len;
-  DL[slot][dlofs+len+1] = 0;
-  return &DL[slot][dlofs];
-}
-
-void dll_add_sprite(word addr, byte x, byte y, byte wpal) {
-  byte slot = (y / SLOTHEIGHT) | slot0;
-  register DL4Entry* dl = (DL4Entry*) dll_alloc(slot, 4);
-  dl->data_lo = (byte)addr;
-  dl->data_hi = (byte)(addr>>8) + (y & 15);
-  dl->xpos = x;
-  dl->width_pal = wpal;
-  if (y & 15) {
-    DL4Entry* dl2 = (DL4Entry*) dll_alloc(slot+1, 4);
-    *dl2 = *dl;
-    dl2->data_hi -= SLOTHEIGHT;
-  }
-}
-
-void dll_add_string(const char* str, byte x, byte y, byte wpal) {
-  byte slot = (y / SLOTHEIGHT) | slot0;
-  register DL5Entry* dl = (DL5Entry*) dll_alloc(slot, 5);
-  dl->data_lo = (byte)str;
-  dl->data_hi = (word)str>>8;
-  dl->flags = DL5_INDIRECT;
-  dl->width_pal = wpal;
-  dl->xpos = x;
-}
-
-void dll_setup() {
-  byte i;
-  byte* dlptr = &DL[0][0];
-  register DLLEntry *dll = &DLL[0];
-  for (i=0; i<NUMSLOTS; i++) {
-    dll->offset_flags = DLL_FLAGS | (SLOTHEIGHT-1);
-    dll->dl_hi = (word)dlptr>>8;
-    dll->dl_lo = (byte)dlptr;
-    dlptr += sizeof(DL[0]);
-    dll++;
-  }
-  dll_clear();
-#ifdef DOUBLEBUFFER
-  dll_swap();
-  dll_clear();
-  dll_swap();
-#endif
-#ifdef DLSAVE
-  memset(DL_save, 0, sizeof(DL_save));
-#endif
-}
-
-// __MAIN__
-
 char* hello = "\2\4\6\0\220\222\102";
 
 void main() {
@@ -164,26 +37,31 @@ void main() {
   MARIA.P1C2 = 0x28;
   MARIA.P1C3 = 0x1f;
   MARIA.BACKGRND = 0;
-  dll_set_addr(DLL);
   MARIA.CTRL = CTRL_DMA_ON | CTRL_DBLBYTE | CTRL_160AB;
 
   dll_clear();
   dll_add_string(hello, y+32, 32, DL_WP(8,0));
   for (i=0; i<8; i++) {
-    slot0 = 0;
+    dll_page(0);
     dll_add_sprite(0xa068, i*4, i*33, DL_WP(4,1));
     dll_add_sprite(0xa06c, i*8, i*25, DL_WP(4,1));
-    slot0 = 16;
+    dll_page(1);
     dll_add_sprite(0xa068, i*4, i*32, DL_WP(4,1));
     dll_add_sprite(0xa06c, 128-i*8, i*24, DL_WP(4,1));
   }
   dll_save();
 
   while (1) {
+    // wait for vsync to end
     while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
     dll_set_scroll(y);
-    dll_restore();
-    dll_add_sprite(0xa06c, y, y, DL_WP(4,1));
+    dll_restore_all();
+    // first sprite doesn't have time to draw when y < 40
+    dll_page(0);
+    dll_add_sprite(0xa06c, y, 128, DL_WP(4,1));
+    dll_page(1);
+    dll_add_sprite(0xa06c, y, 0, DL_WP(4,1));
+    // wait for vsync to start
     while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
     y++;
   }
diff --git a/presets/atari7800/sprites.c b/presets/atari7800/sprites.c
new file mode 100644
index 00000000..2a6341f1
--- /dev/null
+++ b/presets/atari7800/sprites.c
@@ -0,0 +1,88 @@
+
+/*
+This demo sets up two DLLs (Display List Lists) of
+16 slots each.
+
+By swapping between the two DLLs each frame, one DLL can
+be written while the other is displayed.
+*/
+
+#include "atari7800.h"
+#include <string.h>
+#include <stdlib.h>
+
+#include "dll.h"
+//#link "dll.c"
+
+//#link "chr_font.s"
+//#link "generic8x16.s"
+
+#define NUMSPRITES 16
+byte xpos[NUMSPRITES];
+byte ypos[NUMSPRITES];
+
+char* hello = "\2\4\6\0\220\222\102";
+
+// draw a text string randomly into the background
+void draw_background() {
+  byte x = rand();
+  byte y = rand();
+  if (dll_bytesleft(y/SLOTHEIGHT) > 20) {
+    dll_add_string(hello, x, y, DL_WP(7,0));
+    dll_swap();
+    dll_copy();
+    dll_save();
+  }
+}
+
+void main() {
+  byte i;
+  byte y = 0;
+
+  dll_setup();
+  
+  // activate DMA
+  MARIA.CHARBASE = 0x80;
+  MARIA.P0C1 = 0x8f;
+  MARIA.P0C2 = 0x4f;
+  MARIA.P0C3 = 0x1f;
+  MARIA.P1C1 = 0x34;
+  MARIA.P1C2 = 0x28;
+  MARIA.P1C3 = 0x1f;
+  MARIA.BACKGRND = 0;
+  MARIA.CTRL = CTRL_DMA_ON | CTRL_DBLBYTE | CTRL_160AB;
+
+  // set background sprites and save to buffer
+  dll_clear();
+  draw_background();
+  
+  // set up sprite positions randomly
+  for (i=0; i<NUMSPRITES; i++) {
+    xpos[i] = rand();
+    ypos[i] = rand();
+  }
+
+  // frame loop
+  while (1) {
+    // wait for vsync to end
+    while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
+    // swap buffers and restore background
+    dll_swap();
+    dll_restore();
+    // draw new background sprite?
+    // after 32 bytes, the display slots fill up
+    if ((rand() & 255) == 0) {
+      draw_background();
+    }
+    // draw forgeground sprites
+    for (i=0; i<NUMSPRITES; i++) {
+      dll_add_sprite(0xa06c, xpos[i], ypos[i], DL_WP(4,1));
+      xpos[i] += rand() & 3;
+      ypos[i] += rand() & 3;
+    }
+    // wait for vsync to start
+    while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
+    y++;
+  }
+}
+
diff --git a/src/platform/atari7800.ts b/src/platform/atari7800.ts
index 51d1d5de..8901a422 100644
--- a/src/platform/atari7800.ts
+++ b/src/platform/atari7800.ts
@@ -6,6 +6,7 @@ import { PLATFORMS } from "../common/emu";
 var Atari7800_PRESETS = [
   {id:'sprites.dasm', name:'Sprites (ASM)'},
   {id:'wsync.c', name:'WSYNC'},
+  {id:'sprites.c', name:'Double Buffering'},
   {id:'scroll.c', name:'Scrolling'},
 ];