diff --git a/sources/APU/APU.cpp b/sources/APU/APU.cpp
index cdf06f4..be4d9a6 100644
--- a/sources/APU/APU.cpp
+++ b/sources/APU/APU.cpp
@@ -5,6 +5,7 @@
 #include "APU.hpp"
 #include "../Exceptions/NotImplementedException.hpp"
 #include "../Exceptions/InvalidAddress.hpp"
+#include "../Exceptions/InvalidOpcode.hpp"
 
 namespace ComSquare::APU
 {
@@ -47,8 +48,21 @@ namespace ComSquare::APU
 		}
 	}
 
-	bool APU::update()
+	int APU::executeInstruction()
 	{
-		throw NotImplementedException();
+		uint8_t opcode = read(this->_internalRegisters.pc++);
+
+		switch (opcode) {
+		default:
+			throw InvalidOpcode("APU", opcode);
+		}
+	}
+
+	int APU::update()
+	{
+		int cycles = 0;
+
+		cycles += executeInstruction();
+		return cycles;
 	}
 }
diff --git a/sources/APU/APU.hpp b/sources/APU/APU.hpp
index 6c67a8f..f700508 100644
--- a/sources/APU/APU.hpp
+++ b/sources/APU/APU.hpp
@@ -112,6 +112,10 @@ namespace ComSquare::APU
 
 		//! @brief The DSP component used to produce sound
 		std::shared_ptr<DSP::DSP> _dsp;
+
+		//! @brief Execute a single instruction.
+		//! @return The number of cycles that the instruction took.
+		int executeInstruction();
 	public:
 		explicit APU();
 
@@ -125,7 +129,9 @@ namespace ComSquare::APU
 		//! @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();
+		//! @brief This function execute the instructions received.
+		//! @return The number of cycles that elapsed.
+		int update();
 	};
 }