diff --git a/BizHawk.Emulation.Cores/Consoles/Atari/2600/Mappers/m0840.cs b/BizHawk.Emulation.Cores/Consoles/Atari/2600/Mappers/m0840.cs
index 5ff0bc572c..51a71e0543 100644
--- a/BizHawk.Emulation.Cores/Consoles/Atari/2600/Mappers/m0840.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Atari/2600/Mappers/m0840.cs
@@ -1,4 +1,4 @@
-using System;
+using BizHawk.Common;
 
 namespace BizHawk.Emulation.Cores.Atari.Atari2600
 {
@@ -23,9 +23,59 @@ namespace BizHawk.Emulation.Cores.Atari.Atari2600
 	*/
 	internal class m0840 : MapperBase 
 	{
-		public m0840()
+		private int _bank4K;
+
+		private byte ReadMem(ushort addr, bool peek)
 		{
-			throw new NotImplementedException();
+			if (!peek)
+			{
+				Address(addr);
+			}
+
+			if (addr < 0x1000)
+			{
+				return base.ReadMemory(addr);
+			}
+
+			return core.rom[(_bank4K << 12) + (addr & 0xFFF)];
+		}
+
+		public override byte ReadMemory(ushort addr)
+		{
+			return ReadMem(addr, false);
+		}
+
+		public override byte PeekMemory(ushort addr)
+		{
+			return ReadMem(addr, true);
+		}
+
+		public override void WriteMemory(ushort addr, byte value)
+		{
+			Address(addr);
+			if (addr < 0x1000)
+			{
+				base.WriteMemory(addr, value);
+			}
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			base.SyncState(ser);
+			ser.Sync("bank_4k", ref _bank4K);
+		}
+
+		private void Address(ushort addr)
+		{
+			switch (addr & 0x1840)
+			{
+				case 0x0800:
+					_bank4K = 0;
+					break;
+				case 0x0840:
+					_bank4K = 1;
+					break;
+			}
 		}
 	}
 }
diff --git a/output/gamedb/gamedb_a2600.txt b/output/gamedb/gamedb_a2600.txt
index 2ef25837ef..9f1c2787d6 100644
--- a/output/gamedb/gamedb_a2600.txt
+++ b/output/gamedb/gamedb_a2600.txt
@@ -2696,4 +2696,5 @@ sha1:3797959E4A3236B6562CE15AF7D96633F6720FC8		Fu Kung! - 2 Dancing Babies Demo
 sha1:95D67B058EC40E8C5525365714D221E4C6B3C97D		Ruby Runner Demo (4A50 Bankswitching) (2006) (John Payson) (WIP)	A26		m=4A50
 sha1:9CD8217DCCBE60F9A25A930D614EE5384F432A83		Boulder Dash (2005) (Andrew Davie) (WIP)	A26		m=3E
 sha1:00CCF622E7BA4D0A39DCBABAB771CE815B0FB8FE		Boulder Dash (2005) (Andrew Davie) (WIP) (PAL	A26		m=3E
-sha1:650DA2339D41D1D2F180A6CAFE8DC311AC588ACD		Boulder Dash Intro Tune (2005) (Erik Ehrling)	A26		m=3E
\ No newline at end of file
+sha1:650DA2339D41D1D2F180A6CAFE8DC311AC588ACD		Boulder Dash Intro Tune (2005) (Erik Ehrling)	A26		m=3E
+sha1:F28E52921646A18467577370808454F494C15EFE		0840 EconoBanking	A26		m=0840
\ No newline at end of file