diff --git a/Core/FDS.cpp b/Core/FDS.cpp
index 7cd880fe..e1cfacf1 100644
--- a/Core/FDS.cpp
+++ b/Core/FDS.cpp
@@ -375,12 +375,15 @@ bool FDS::IsDiskInserted()
 
 uint8_t FDS::ReadRegister(uint16_t addr)
 {
-	uint8_t value = 0;
+	uint8_t value = MemoryManager::GetOpenBus();
 	if(_soundRegEnabled && addr >= 0x4040) {
 		return _audio->ReadRegister(addr);
 	} else if(_diskRegEnabled && addr <= 0x4033) {
 		switch(addr) {
 			case 0x4030:
+				//These 3 pins are open bus
+				value &= 0x2C;
+
 				value |= CPU::HasIRQSource(IRQSource::External) ? 0x01 : 0x00;
 				value |= _transferComplete ? 0x02 : 0x00;
 				value |= _badCrc ? 0x10 : 0x00;
@@ -398,6 +401,9 @@ uint8_t FDS::ReadRegister(uint16_t addr)
 				return _readDataReg;
 
 			case 0x4032:
+				//These 5 pins are open bus
+				value &= 0xF8;
+
 				value |= !IsDiskInserted() ? 0x01 : 0x00;  //Disk not in drive
 				value |= (!IsDiskInserted() || !_scanningDisk) ? 0x02 : 0x00;  //Disk not ready
 				value |= !IsDiskInserted() ? 0x04 : 0x00;  //Disk not writable
@@ -413,7 +419,7 @@ uint8_t FDS::ReadRegister(uint16_t addr)
 
 			case 0x4033:
 				//Always return good battery
-				return 0x80 & _extConWriteReg;
+				return _extConWriteReg;
 		}
 	}
 
diff --git a/Core/FdsAudio.h b/Core/FdsAudio.h
index 3b1ea6ca..ab0740ff 100644
--- a/Core/FdsAudio.h
+++ b/Core/FdsAudio.h
@@ -90,16 +90,19 @@ protected:
 public:
 	uint8_t ReadRegister(uint16_t addr)
 	{
+		uint8_t value = MemoryManager::GetOpenBus();
 		if(addr <= 0x407F) {
-			return 0x40 | _waveTable[addr & 0x3F];
-		} else {
-			switch(addr) {
-				case 0x4090: return 0x40 | _volume.GetGain();
-				case 0x4092: return 0x40 | _mod.GetGain();
-			}
+			value &= 0xC0;
+			value |= _waveTable[addr & 0x3F];
+		} else if(addr == 0x4090) {
+			value &= 0xC0;
+			value |= _volume.GetGain();
+		} else if(addr == 0x4092) {
+			value &= 0xC0;
+			value |= _mod.GetGain();
 		}
 
-		return MemoryManager::GetOpenBus();
+		return value;
 	}
 
 	void WriteRegister(uint16_t addr, uint8_t value)