diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CNROM.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CNROM.cs
index 66e3cab99c..41155a9371 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CNROM.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/CNROM.cs
@@ -11,32 +11,17 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 	//Bump 'n' Jump
 	//Cybernoid
 
-	/*
-	 * What's going on here?
-	 * 
-	 * 1. Security Diode should include all Mapper185 carts, but they aren't included?
-	 * 2. Good luck ever getting bus conflicts right, considering all of the third party crap overloaded onto this mapper.
-	 * 3. (Minor) Configuration shouldn't be serialized.
-	 * 4. What is prg_mask?  It's obviously a mask for swapping 16K prg banks... which this board never does.
-	 * 5. Like on real CNROM, the reg writes are masked so only the lowest 2 bits show.  But then:
-	 * 5a. AssertChr(64); could never be handled correctly by this class.
-	 * 5b. The copy protection check compares on bits of the chr reg that are always 0.  Nonsensical.
-	 * 5c. The real cart's security diodes, which are connected to higher data bits, are never actually read.
-	 * 6. chr_enabled is forced to true after any PPU read, which is wrong.  Probably a hack for #5; since the real security setting is never used.
-	 * 7. Related to 5a; the AVE-74*161 implementation is busted.
-	 */
-
 	[NES.INESBoardImplPriority]
 	public sealed class CNROM : NES.NESBoardBase
 	{
 		//configuration
-		int prg_mask,chr_mask;
-		bool copyprotection;
-		bool chr_enabled = true;
+		int prg_byte_mask, chr_mask;
+		bool copyprotection = false;
 		bool bus_conflict;
 
 		//state
 		int chr;
+		bool chr_enabled = true;
 
 		public override bool Configure(NES.EDetectionOrigin origin)
 		{
@@ -44,19 +29,25 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 			switch (Cart.board_type)
 			{
 				case "MAPPER185":
+				case "HVC-CNROM+SECURITY":
+					copyprotection = true;
+					bus_conflict = true;
+					AssertPrg(16, 32); AssertChr(8);
+					break;
 				case "MAPPER003":
 					//we assume no bus conflicts for generic unknown cases.
 					//this was done originally to support Colorful Dragon (Unl) (Sachen) which bugs out if bus conflicts are emulated
 					//Games which behave otherwise will force us to start entering these in the game DB
 					//Licensed titles below are more likely to have used the same original discrete logic design and so suffer from the conflicts
 					bus_conflict = false;
+					AssertPrg(8, 16, 32);
 					break;
-				
+
 				case "NES-CNROM": //adventure island
 				case "UNIF_NES-CNROM": // some of these should be bus_conflict = false because UNIF is bad
 				case "HVC-CNROM":
 					bus_conflict = true;
-					AssertPrg(16, 32); AssertChr(8,16,32,64);
+					AssertPrg(16, 32);
 					break;
 				case "KONAMI-CNROM": //gradius (J)
 					bus_conflict = true;
@@ -68,28 +59,26 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 					break;
 				default:
 					return false;
-
 			}
 			if (Cart.pcb == "HVC-CNROM-256K-01")
 				copyprotection = true;
-			else
-				copyprotection = false;
-			prg_mask = (Cart.prg_size / 16) - 1;
+			prg_byte_mask = Cart.prg_size * 1024 - 1;
 			chr_mask = (Cart.chr_size / 8) - 1;
 			SetMirrorType(Cart.pad_h, Cart.pad_v);
 
 			return true;
 		}
-		
+
 		public override void WritePRG(int addr, byte value)
 		{
-			if (bus_conflict) value = HandleNormalPRGConflict(addr,value);
-			value &= 3;
-			chr = value&chr_mask;
+			if (bus_conflict)
+				value = HandleNormalPRGConflict(addr, value);
+
+			chr = value & chr_mask;
 
 			if (copyprotection)
 			{
-				if ((chr & 0x0F) > 0 && (chr != 0x13))
+				if ((value & 0x0F) > 0 && (value != 0x13))
 				{
 					chr_enabled = true;
 					Console.WriteLine("chr enabled");
@@ -100,45 +89,34 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 					Console.WriteLine("chr disabled");
 				}
 			}
-			//Console.WriteLine("at {0}, set chr={1}", NES.ppu.ppur.status.sl, chr);
 		}
 
 		public override byte ReadPPU(int addr)
 		{
 			if (chr_enabled == false)
 			{
-				chr_enabled = true;
 				return 0x12;
 			}
 			if (addr < 0x2000)
 			{
-				return VROM[addr + (chr<<13)];
+				return VROM[addr + (chr << 13)];
+			}
+			else
+			{
+				return base.ReadPPU(addr);
 			}
-			else return base.ReadPPU(addr);
 		}
 
 		public override void SyncState(Serializer ser)
 		{
 			base.SyncState(ser);
-			ser.Sync("chr",ref chr);
-			ser.Sync("copyprotection", ref copyprotection);
-			ser.Sync("prg_mask", ref prg_mask);
-			ser.Sync("chr_mask", ref chr_mask);
-			ser.Sync("bus_conflict", ref bus_conflict);
+			ser.Sync("chr", ref chr);
+			ser.Sync("chr_enabled", ref chr_enabled);
 		}
 
 		public override byte ReadPRG(int addr)
 		{
-			if (prg_mask > 0)
-			{
-				return ROM[addr];
-			}
-			else
-			{
-				return ROM[addr & 0x3FFF]; //adelikat: Keeps Bird Week from crashing (only 16k PRG), but it doesn't work
-			}
-			
+			return ROM[addr & prg_byte_mask];
 		}
-
 	}
-}
\ No newline at end of file
+}
diff --git a/output/gamedb/NesCarts.7z b/output/gamedb/NesCarts.7z
index d3261505f9..f881ed0efb 100644
Binary files a/output/gamedb/NesCarts.7z and b/output/gamedb/NesCarts.7z differ