diff --git a/sources/APU/APU.cpp b/sources/APU/APU.cpp
index c459992..50b8750 100644
--- a/sources/APU/APU.cpp
+++ b/sources/APU/APU.cpp
@@ -2,3 +2,97 @@
 // Created by Melefo on 27/01/2020.
 //
 
+#include "APU.hpp"
+#include "../Exceptions/NotImplementedException.hpp"
+#include "../Exceptions/InvalidAddress.hpp"
+
+namespace ComSquare::APU
+{
+	APU::APU(std::shared_ptr<DSP> dsp)
+			: _dsp(std::move(dsp))
+	{ }
+
+	uint8_t APU::read(uint24_t addr)
+	{
+		switch (addr) {
+		case 0xF0:
+			return this->_internalRegisters.unknown;
+		case 0xF2:
+			return this->_internalRegisters.dspregAddr;
+		case 0xF3:
+			return this->_internalRegisters.dspregData;
+		case 0xF4:
+			return this->_internalRegisters.port0;
+		case 0xF5:
+			return this->_internalRegisters.port1;
+		case 0xF6:
+			return this->_internalRegisters.port2;
+		case 0xF7:
+			return this->_internalRegisters.port3;
+		case 0xF8:
+			return this->_internalRegisters.regmem1;
+		case 0xF9:
+			return this->_internalRegisters.regmem2;
+		case 0xFD:
+			return this->_internalRegisters.counter0;
+		case 0xFE:
+			return this->_internalRegisters.counter1;
+		case 0xFF:
+			return this->_internalRegisters.counter2;
+		default:
+			throw InvalidAddress("APU Internal Registers read", addr);
+		}
+	}
+
+	void APU::write(uint24_t addr, uint8_t data)
+	{
+		switch (addr) {
+		case 0xF0:
+			this->_internalRegisters.unknown = data;
+			break;
+		case 0xF1:
+			this->_internalRegisters.ctrlreg = data;
+			break;
+		case 0xF2:
+			this->_internalRegisters.dspregAddr = data;
+			break;
+		case 0xF3:
+			this->_internalRegisters.dspregData = data;
+			break;
+		case 0xF4:
+			this->_internalRegisters.port0 = data;
+			break;
+		case 0xF5:
+			this->_internalRegisters.port1 = data;
+			break;
+		case 0xF6:
+			this->_internalRegisters.port2 = data;
+			break;
+		case 0xF7:
+			this->_internalRegisters.port3 = data;
+			break;
+		case 0xF8:
+			this->_internalRegisters.regmem1 = data;
+			break;
+		case 0xF9:
+			this->_internalRegisters.regmem2 = data;
+			break;
+		case 0xFA:
+			this->_internalRegisters.timer0 = data;
+			break;
+		case 0xFB:
+			this->_internalRegisters.timer1 = data;
+			break;
+		case 0xFC:
+			this->_internalRegisters.timer2 = data;
+			break;
+		default:
+			throw InvalidAddress("APU Internal Registers write", addr);
+		}
+	}
+
+	bool APU::update()
+	{
+		throw NotImplementedException();
+	}
+}
diff --git a/sources/APU/APU.hpp b/sources/APU/APU.hpp
index a882ce1..af75bf3 100644
--- a/sources/APU/APU.hpp
+++ b/sources/APU/APU.hpp
@@ -5,30 +5,37 @@
 #ifndef COMSQUARE_APU_HPP
 #define COMSQUARE_APU_HPP
 
+#include <memory>
 #include "../Memory/IMemory.hpp"
 
 namespace ComSquare::APU
 {
 	struct Registers {
-		//! @brief The Accumulator register
-		unsigned char a;
 
 		//! @brief The X index register
-		unsigned char x;
+		uint8_t x;
 
-		//! @brief The Y index register
-		unsigned char y;
+		//! @brief The YA register
+		union {
+			struct {
+				//! @brief The Accumulator register
+				uint8_t a;
+				//! @brief The Y Index register
+				uint8_t y;
+			};
+			uint16_t ya;
+		};
 
 		//! @brief The Stack pointer register
-		unsigned char sp;
+		uint8_t sp;
 
 		//! @brief The Program counter register
 		union {
 			struct {
-				unsigned char pch;
-				unsigned char pcl;
+				uint8_t pcl;
+				uint8_t pch;
 			};
-			unsigned short pc;
+			uint16_t pc;
 		};
 
 		//! @brief Program Status Word register
@@ -52,9 +59,66 @@ namespace ComSquare::APU
 		};
 	};
 
+	struct InternalRegisters
+	{
+		//! @brief An undocumented register
+		uint8_t unknown;
+
+		//! @brief Control Register register
+		uint8_t ctrlreg;
+
+		//! @brief DSP Register Address register
+		uint8_t dspregAddr;
+		//! @brief DSP Register data register
+		uint8_t dspregData;
+
+		//! @brief Port 0 register
+		uint8_t port0;
+		//! @brief Port 1 register
+		uint8_t port1;
+		//! @brief Port 2 register
+		uint8_t port2;
+		//! @brief Port 3 register
+		uint8_t port3;
+
+		//! @brief Regular Memory register
+		uint8_t regmem1;
+		//! @brief Another Regular Memory register
+		uint8_t regmem2;
+
+		//! @brief Timer-0 register
+		uint8_t timer0;
+		//! @brief Timer-1 register
+		uint8_t timer1;
+		//! @brief Timer-2 register
+		uint8_t timer2;
+
+		//! @brief Counter-0 register
+		uint8_t counter0;
+		//! @brief Counter-1 register
+		uint8_t counter1;
+		//! @brief Counter-2 register
+		uint8_t counter2;
+
+	};
+
+
 	class APU : IMemory {
 	private:
 		Registers _registers;
+		InternalRegisters _internalRegisters{};
+	public:
+		//! @brief Read from the internal APU register.
+		//! @param addr The address to read from. The address 0xF0 should refer to the first byte of the register.
+		//! @throw InvalidAddress will be thrown if the address is more than $FF (the number of register).
+		//! @return Return the value of the register.
+		uint8_t read(uint24_t addr) override;
+		//! @brief Write data to the internal APY register.
+		//! @param addr The address to write to. The address 0xF0 should refer to the first byte of register.
+		//! @param data The new value of the register.
+		//! @throw InvalidAddress will be thrown if the address is more than $FF (the number of register).
+		void write(uint24_t addr, uint8_t data) override;
+		bool update();
 	};
 }