diff --git a/presets/nes/fami.c b/presets/nes/fami.c
index cdf9b7f5..05e6f29b 100644
--- a/presets/nes/fami.c
+++ b/presets/nes/fami.c
@@ -9,6 +9,8 @@ Press controller buttons to hear sound effects.
 // link the pattern table into CHR ROM
 //#link "chr_generic.s"
 
+// setup Famitone library
+
 //#link "famitone2.s"
 void __fastcall__ famitone_update(void);
 //#link "music_aftertherain.s"
@@ -29,7 +31,7 @@ void main(void)
   //famitone_init(after_the_rain_music_data);
   famitone_init(danger_streets_music_data);
   sfx_init(demo_sounds);
-  // set music callback
+  // set music callback function for NMI
   nmi_set_callback(famitone_update);
   // play music
   music_play(0);
diff --git a/presets/nes/horizscroll.c b/presets/nes/horizscroll.c
index 1f210cec..f56c9cb2 100644
--- a/presets/nes/horizscroll.c
+++ b/presets/nes/horizscroll.c
@@ -140,6 +140,7 @@ void update_offscreen() {
   }
 }
 
+// scrolls the screen left one pixel
 void scroll_left() {
   // update nametable every 16 pixels
   if ((x_scroll & 15) == 0) {
@@ -149,7 +150,7 @@ void scroll_left() {
   ++x_scroll;
 }
 
-// function to scroll window up and down until end
+// main loop, scrolls left continuously
 void scroll_demo() {
   // get data for initial segment
   new_segment();
@@ -159,7 +160,7 @@ void scroll_demo() {
     // ensure VRAM buffer is cleared
     ppu_wait_nmi();
     vrambuf_clear();
-    // split at x_scroll
+    // split at sprite zero and set X scroll
     split(x_scroll, 0);
     // scroll to the left
     scroll_left();
diff --git a/presets/nes/monobitmap.c b/presets/nes/monobitmap.c
index a25c7d9a..8c0dc004 100644
--- a/presets/nes/monobitmap.c
+++ b/presets/nes/monobitmap.c
@@ -16,11 +16,13 @@ that display their own pixels.
 
 bool ppu_is_on = false;
 
+// simple 6502 delay loop (5 cycles per loop)
 #define DELAYLOOP(n) \
   __asm__("ldy #%b", n); \
   __asm__("@1: dey"); \
   __asm__("bne @1");
 
+// call every frame to split screen
 void monobitmap_split() {
   // split screen at line 128
   split(0,0);
@@ -28,6 +30,7 @@ void monobitmap_split() {
   PPU.control = PPU.control ^ 0x10; // bg bank 1
 }
 
+// set a pixel at (x,y) color 1=set, 0=clear
 void monobitmap_set_pixel(byte x, byte y, byte color) {
   byte b;
   // compute pattern table address
@@ -56,6 +59,7 @@ void monobitmap_set_pixel(byte x, byte y, byte color) {
   }
 }
 
+// draw a line from (x0,y0) to (x1,y1)
 void monobitmap_draw_line(int x0, int y0, int x1, int y1, byte color) {
   int dx = abs(x1-x0);
   int sx = x0<x1 ? 1 : -1;
@@ -72,24 +76,26 @@ void monobitmap_draw_line(int x0, int y0, int x1, int y1, byte color) {
   }
 }
 
-// write values 0..255
+// write values 0..255 to nametable
 void monobitmap_put_256inc() {
   word i;
   for (i=0; i<256; i++)
     vram_put(i);
 }
 
+// sets up attribute table
 void monobitmap_put_attrib() {
   vram_fill(0x00, 0x10); // first palette
   vram_fill(0x55, 0x10); // second palette
 }
 
+// clears pattern table
 void monobitmap_clear() {
-  // clear pattern table
   vram_adr(0x0);
   vram_fill(0x0, 0x2000);
 }
 
+// sets up PPU for monochrome bitmap
 void monobitmap_setup() {
   monobitmap_clear();
   // setup nametable A and B
@@ -123,6 +129,7 @@ const byte MONOBMP_PALETTE[16] = {
   0x03, 0x30, 0x30
 };
 
+// demo function, draws a bunch of lines
 void monobitmap_demo() {
   byte i;
   static const byte x1 = 16;
@@ -147,17 +154,21 @@ void monobitmap_demo() {
 
 void main(void)
 {
+  // setup and draw some lines
   monobitmap_setup();
   pal_bg(MONOBMP_PALETTE);
   monobitmap_demo();
   ppu_on_all();
+  // wait for key press
   while (!pad_trigger(0)) {
     ppu_wait_nmi();
     monobitmap_split();
   }
+  // set up again
   ppu_off();
   monobitmap_setup();
   ppu_on_all();
+  // realtime display where 1 pixel per frame
   ppu_is_on = true;
   monobitmap_demo();
   while(1) {
diff --git a/src/platform/nes.ts b/src/platform/nes.ts
index 0879eb59..e703bfed 100644
--- a/src/platform/nes.ts
+++ b/src/platform/nes.ts
@@ -19,12 +19,12 @@ const JSNES_PRESETS = [
   {id:'metacursor.c', name:'Controllers'},
   {id:'vrambuffer.c', name:'VRAM Buffer'},
   {id:'statusbar.c', name:'Split Status Bar'},
-  {id:'horizscroll.c', name:'Offscreen Scrolling'},
   {id:'siegegame.c', name:'Siege Game'},
   {id:'tint.c', name:'Color Emphasis'},
   {id:'rletitle.c', name:'Title Screen RLE'},
   {id:'aputest.c', name:'Sound Tester'},
   {id:'music.c', name:'Music Player'},
+  {id:'horizscroll.c', name:'Offscreen Scrolling'},
   {id:'monobitmap.c', name:'Monochrome Bitmap'},
   {id:'fami.c', name:'Famitone Demo'},
   {id:'shoot2.c', name:'Solarian Game'},