From f22c9b7abd61bb0dca111e5dea02e2679707184d Mon Sep 17 00:00:00 2001
From: SaxxonPike <saxxonpike@gmail.com>
Date: Sat, 13 Jul 2019 15:25:40 -0500
Subject: [PATCH] C64: CPU reads open bus when !AEC is asserted

---
 .../Computers/Commodore64/C64.Motherboard.cs                   | 1 +
 BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Chip6510.cs  | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/BizHawk.Emulation.Cores/Computers/Commodore64/C64.Motherboard.cs b/BizHawk.Emulation.Cores/Computers/Commodore64/C64.Motherboard.cs
index 9151154a5a..8e951246dc 100644
--- a/BizHawk.Emulation.Cores/Computers/Commodore64/C64.Motherboard.cs
+++ b/BizHawk.Emulation.Cores/Computers/Commodore64/C64.Motherboard.cs
@@ -234,6 +234,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64
 			Cpu.ReadMemory = Pla.Read;
 			Cpu.WriteMemory = Pla.Write;
 			Cpu.WriteMemoryPort = Cpu_WriteMemoryPort;
+			Cpu.ReadBus = ReadOpenBus;
 
 			Pla.PeekBasicRom = BasicRom.Peek;
 			Pla.PeekCartridgeHi = CartPort.PeekHiRom;
diff --git a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Chip6510.cs b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Chip6510.cs
index a79632d865..a4343f44fc 100644
--- a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Chip6510.cs
+++ b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Chip6510.cs
@@ -41,6 +41,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 		public Func<bool> ReadIrq;
 		public Func<bool> ReadNmi;
 		public Func<bool> ReadRdy;
+		public Func<int> ReadBus;
 		public Func<int, int> ReadMemory;
 		public Func<int> ReadPort;
 		public Action<int, int> WriteMemory;
@@ -136,7 +137,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 				case 0x0001:
 					return PortData;
 				default:
-					return ReadAec() ? ReadMemory(addr) : 0xFF;
+					return ReadAec() ? ReadMemory(addr) : ReadBus();
 			}
 		}