diff --git a/src/app/emu/cpu.cc b/src/app/emu/cpu.cc
index b9059677..bcb9e932 100644
--- a/src/app/emu/cpu.cc
+++ b/src/app/emu/cpu.cc
@@ -334,23 +334,23 @@ void CPU::ExecuteInstruction(uint8_t opcode) {
       break;
 
     case 0xE0:  // CPX Immediate
-      // CPX();
+      CPX(Immediate());
       break;
     case 0xE4:  // CPX Direct Page
       // CPX();
       break;
     case 0xEC:  // CPX Absolute
-      // CPX();
+      CPX(Absolute());
       break;
 
     case 0xC0:  // CPY Immediate
-      // CPY();
+      CPY(Immediate());
       break;
     case 0xC4:  // CPY Direct Page
       // CPY();
       break;
     case 0xCC:  // CPY Absolute
-      // CPY();
+      CPY(Absolute());
       break;
 
     case 0x3A:  // DEC Accumulator
@@ -370,11 +370,11 @@ void CPU::ExecuteInstruction(uint8_t opcode) {
       break;
 
     case 0xCA:  // DEX Decrement X register
-      // DEX();
+      DEX();
       break;
 
     case 0x88:  // DEY Decrement Y register
-      // DEY();
+      DEY();
       break;
 
     case 0x41:  // EOR DP Indexed Indirect, X
@@ -951,7 +951,7 @@ void CPU::ExecuteInstruction(uint8_t opcode) {
       break;
 
     case 0xFB:  // XCE
-      // XCE();
+      XCE();
       break;
     default:
       std::cerr << "Unknown instruction: " << std::hex
@@ -962,7 +962,7 @@ void CPU::ExecuteInstruction(uint8_t opcode) {
 
 void CPU::ADC(uint8_t operand) {
   auto C = GetCarryFlag();
-  if (GetAccumulatorSize()) {                         // 8-bit mode
+  if (!E) {                                           // 8-bit mode
     uint16_t result = (A & 0xFF) + (operand & 0xFF);  // + (C ? 1 : 0);
     SetCarryFlag(!(result > 0xFF));                   // Update the carry flag
 
@@ -997,7 +997,7 @@ void CPU::ADC(uint8_t operand) {
 
 void CPU::AND(uint16_t address) {
   uint8_t operand;
-  if (GetAccumulatorSize() == 0) {  // 16-bit mode
+  if (E == 0) {  // 16-bit mode
     uint16_t operand16 = memory.ReadWord(address);
     A &= operand16;
     SetZeroFlag(A == 0);
diff --git a/src/app/emu/cpu.h b/src/app/emu/cpu.h
index 6d047c16..61212ee3 100644
--- a/src/app/emu/cpu.h
+++ b/src/app/emu/cpu.h
@@ -242,14 +242,14 @@ class CPU : public Memory {
   // ==========================================================================
   // Registers
 
-  uint8_t A = 0;  // Accumulator
-  uint8_t X = 0;  // X index register
-  uint8_t Y = 0;  // Y index register
-  // uint8_t SP = 0;   // Stack Pointer
-  uint16_t DB = 0;  // Data Bank register
+  uint8_t A = 0;    // Accumulator
+  uint8_t X = 0;    // X index register
+  uint8_t Y = 0;    // Y index register
   uint16_t D = 0;   // Direct Page register
+  uint16_t DB = 0;  // Data Bank register
   uint16_t PB = 0;  // Program Bank register
   uint16_t PC = 0;  // Program Counter
+  uint8_t E = 1;    // Emulation mode flag
   uint8_t status;   // Processor Status (P)
 
   // Mnemonic 	Value 	Binary 	Description
@@ -312,12 +312,7 @@ class CPU : public Memory {
   // CPX: Compare X register
   // CPY: Compare Y register
   // DEC: Decrement
-  // DEX: Decrement X register
-  // DEY: Decrement Y register
   // EOR: Exclusive OR
-  // INC: Increment
-  // INX: Increment X register
-  // INY: Increment Y register
   // JMP: Jump
   // JML: Jump long
   // JSR: Jump to subroutine
@@ -333,19 +328,6 @@ class CPU : public Memory {
   // PEA: Push effective address
   // PEI: Push effective indirect address
   // PER: Push effective PC-relative address
-  // PHA: Push accumulator
-  // PHB: Push data bank register
-  // PHD: Push direct page register
-  // PHK: Push program bank register
-  // PHP: Push processor status register
-  // PHX: Push X register
-  // PHY: Push Y register
-  // PLA: Pull accumulator
-  // PLB: Pull data bank register
-  // PLD: Pull direct page register
-  // PLP: Pull processor status register
-  // PLX: Pull X register
-  // PLY: Pull Y register
   // ROL: Rotate left
   // ROR: Rotate right
   // RTI: Return from interrupt
@@ -390,16 +372,86 @@ class CPU : public Memory {
     PC++;
   }
 
+  // SEC: Set carry flag
   void SEC() { status |= 0x01; }
 
+  // CLC: Clear carry flag
   void CLC() { status &= ~0x01; }
 
+  // CLD: Clear decimal mode
   void CLD() { status &= ~0x08; }
 
+  // CLI: Clear interrupt disable flag
   void CLI() { status &= ~0x04; }
 
+  // CLV: Clear overflow flag
   void CLV() { status &= ~0x40; }
 
+  bool emulation_mode = false;
+
+  void CPX(uint16_t address) {
+    uint16_t memory_value =
+        E ? memory.ReadByte(address) : memory.ReadWord(address);
+    compare(X, memory_value);
+  }
+
+  void CPY(uint16_t address) {
+    uint16_t memory_value =
+        E ? memory.ReadByte(address) : memory.ReadWord(address);
+    compare(Y, memory_value);
+  }
+
+  // DEX: Decrement X register
+  void DEX() {
+    X--;
+    SetZeroFlag(X == 0);
+    SetNegativeFlag(X & 0x80);
+  }
+
+  // DEY: Decrement Y register
+  void DEY() {
+    Y--;
+    SetZeroFlag(Y == 0);
+    SetNegativeFlag(Y & 0x80);
+  }
+
+  // INX: Increment X register
+  void INX() {
+    X++;
+    SetNegativeFlag(X & 0x80);
+    SetZeroFlag(X == 0);
+  }
+
+  // INY: Increment Y register
+  void INY() {
+    Y++;
+    SetNegativeFlag(Y & 0x80);
+    SetZeroFlag(Y == 0);
+  }
+
+  // INC: Increment memory
+  void INC(uint16_t address) {
+    if (GetAccumulatorSize()) {
+      uint8_t value = ReadByte(address);
+      value++;
+      if (value == static_cast<uint8_t>(0x100)) {
+        value = 0x00;  // Wrap around in 8-bit mode
+      }
+      WriteByte(address, value);
+      SetNegativeFlag(value & 0x80);
+      SetZeroFlag(value == 0);
+    } else {
+      uint16_t value = ReadWord(address);
+      value++;
+      if (value == static_cast<uint16_t>(0x10000)) {
+        value = 0x0000;  // Wrap around in 16-bit mode
+      }
+      WriteByte(address, value);
+      SetNegativeFlag(value & 0x80);
+      SetZeroFlag(value == 0);
+    }
+  }
+
   // Push Accumulator on Stack
   void PHA() { memory.PushByte(A); }
 
@@ -535,19 +587,22 @@ class CPU : public Memory {
     SetNegativeFlag(A & 0x80);
   }
 
-  void INX() {
-    X++;
-    SetZeroFlag(X == 0);
-    SetNegativeFlag(X & 0x80);
-  }
-
-  void INY() {
-    Y++;
-    SetZeroFlag(Y == 0);
-    SetNegativeFlag(Y & 0x80);
+  // XCE: Exchange Carry and Emulation Flags
+  void XCE() {
+    uint8_t carry = status & 0x01;
+    status &= ~0x01;
+    status |= E;
+    E = carry;
   }
 
  private:
+  void compare(uint16_t register_value, uint16_t memory_value) {
+    uint16_t result = register_value - memory_value;
+    SetNegativeFlag(result & (E ? 0x8000 : 0x80));  // Negative flag
+    SetZeroFlag(result == 0);                       // Zero flag
+    SetCarryFlag(register_value >= 0);              // Carry flag
+  }
+
   // Helper function to set or clear a specific flag bit
   void SetFlag(uint8_t mask, bool set) {
     if (set) {
diff --git a/src/app/emu/mem.h b/src/app/emu/mem.h
index 828676db..d4cb5ee6 100644
--- a/src/app/emu/mem.h
+++ b/src/app/emu/mem.h
@@ -74,8 +74,8 @@ class MemoryImpl : public Memory {
   }
 
   void WriteByte(uint32_t address, uint8_t value) override {
-    uint32_t mapped_address = GetMappedAddress(address);
-    memory_.at(mapped_address) = value;
+   // uint32_t mapped_address = GetMappedAddress(address);
+    memory_[address] = value;
   }
   void WriteWord(uint32_t address, uint16_t value) override {
     uint32_t mapped_address = GetMappedAddress(address);
diff --git a/test/cpu_test.cc b/test/cpu_test.cc
index 0800fcc0..beca912d 100644
--- a/test/cpu_test.cc
+++ b/test/cpu_test.cc
@@ -36,6 +36,9 @@ class MockMemory : public Memory {
   void SetMemoryContents(const std::vector<uint8_t>& data) {
     memory_.resize(64000);
     std::copy(data.begin(), data.end(), memory_.begin());
+  }
+
+  void Init() {
     ON_CALL(*this, ReadByte(::testing::_))
         .WillByDefault(
             [this](uint16_t address) { return memory_.at(address); });
@@ -50,6 +53,15 @@ class MockMemory : public Memory {
                  (static_cast<uint32_t>(memory_.at(address + 1)) << 8) |
                  (static_cast<uint32_t>(memory_.at(address + 2)) << 16);
         });
+    ON_CALL(*this, WriteByte(::testing::_, ::testing::_))
+        .WillByDefault([this](uint32_t address, uint8_t value) {
+          memory_[address] = value;
+        });
+    ON_CALL(*this, WriteWord(::testing::_, ::testing::_))
+        .WillByDefault([this](uint32_t address, uint16_t value) {
+          memory_[address] = value & 0xFF;
+          memory_[address + 1] = (value >> 8) & 0xFF;
+        });
     ON_CALL(*this, PushByte(::testing::_)).WillByDefault([this](uint8_t value) {
       memory_.at(SP_) = value;
     });
@@ -69,6 +81,9 @@ class MockMemory : public Memory {
       this->SetSP(SP_ + 2);
       return value;
     });
+    ON_CALL(*this, ClearMemory()).WillByDefault([this]() {
+      memory_.resize(64000, 0x00);
+    });
   }
 
  private:
@@ -78,6 +93,11 @@ class MockMemory : public Memory {
 
 class CPUTest : public ::testing::Test {
  public:
+  void SetUp() override {
+    mock_memory.Init();
+    mock_memory.ClearMemory();
+  }
+
   MockMemory mock_memory;
   CPU cpu{mock_memory};
 };
@@ -239,9 +259,10 @@ TEST_F(CPUTest, AND_Immediate) {
   EXPECT_EQ(cpu.A, 0b10100000);  // A register should now be 0b10100000
 }
 
-TEST_F(CPUTest, AND_Absolute) {
+TEST_F(CPUTest, AND_Absolute_16BitMode) {
   cpu.A = 0b11111111;  // A register
-  cpu.status = 0x00;   // 16-bit mode
+  cpu.E = 0;           // 16-bit mode
+  cpu.status = 0x00;   // Clear status flags
   cpu.PC = 1;          // PC register
   std::vector<uint8_t> data = {0x2D, 0x03, 0x00, 0b10101010, 0x01, 0x02};
   mock_memory.SetMemoryContents(data);
@@ -310,6 +331,142 @@ TEST_F(CPUTest, BRL) {
   EXPECT_EQ(cpu.PC, 0x1004);
 }
 
+// ============================================================================
+
+// Test for CPX instruction
+TEST_F(CPUTest, CPX_CarryFlagSet) {
+  cpu.X = 0x1000;
+  cpu.CPX(0x0F00);
+  ASSERT_TRUE(cpu.GetCarryFlag());  // Carry flag should be set
+}
+
+TEST_F(CPUTest, CPX_ZeroFlagSet) {
+  cpu.X = 0x0F00;
+  cpu.ExecuteInstruction(0xE0);    // Immediate CPX
+  ASSERT_TRUE(cpu.GetZeroFlag());  // Zero flag should be set
+}
+
+TEST_F(CPUTest, CPX_NegativeFlagSet) {
+  cpu.PC = 1;
+  cpu.X = 0x8000;
+  std::vector<uint8_t> data = {0xE0, 0xFF, 0xFF};
+  mock_memory.SetMemoryContents(data);
+
+  cpu.ExecuteInstruction(0xE0);  // Immediate CPX (0xFFFF)
+
+  ASSERT_TRUE(cpu.GetNegativeFlag());  // Negative flag should be set
+}
+
+// Test for CPY instruction
+TEST_F(CPUTest, CPY_CarryFlagSet) {
+  cpu.Y = 0x1000;
+  cpu.CPY(0x0F00);
+  ASSERT_TRUE(cpu.GetCarryFlag());  // Carry flag should be set
+}
+
+TEST_F(CPUTest, CPY_ZeroFlagSet) {
+  cpu.Y = 0x0F00;
+  cpu.CPY(0x0F00);
+  ASSERT_TRUE(cpu.GetZeroFlag());  // Zero flag should be set
+}
+
+TEST_F(CPUTest, CPY_NegativeFlagSet) {
+  cpu.PC = 1;
+  cpu.Y = 0x8000;
+  std::vector<uint8_t> data = {0xC0, 0xFF, 0xFF};
+  mock_memory.SetMemoryContents(data);
+  cpu.ExecuteInstruction(0xC0);        // Immediate CPY (0xFFFF)
+  ASSERT_TRUE(cpu.GetNegativeFlag());  // Negative flag should be set
+}
+
+// ============================================================================
+// DEC - Decrement Memory
+
+// Test for DEX instruction
+TEST_F(CPUTest, DEX) {
+  cpu.X = 0x02;                  // Set X register to 2
+  cpu.ExecuteInstruction(0xCA);  // Execute DEX instruction
+  EXPECT_EQ(0x01, cpu.X);  // Expected value of X register after decrementing
+
+  cpu.X = 0x00;                  // Set X register to 0
+  cpu.ExecuteInstruction(0xCA);  // Execute DEX instruction
+  EXPECT_EQ(0xFF, cpu.X);  // Expected value of X register after decrementing
+
+  cpu.X = 0x80;                  // Set X register to 128
+  cpu.ExecuteInstruction(0xCA);  // Execute DEX instruction
+  EXPECT_EQ(0x7F, cpu.X);  // Expected value of X register after decrementing
+}
+
+// Test for DEY instruction
+TEST_F(CPUTest, DEY) {
+  cpu.Y = 0x02;                  // Set Y register to 2
+  cpu.ExecuteInstruction(0x88);  // Execute DEY instruction
+  EXPECT_EQ(0x01, cpu.Y);  // Expected value of Y register after decrementing
+
+  cpu.Y = 0x00;                  // Set Y register to 0
+  cpu.ExecuteInstruction(0x88);  // Execute DEY instruction
+  EXPECT_EQ(0xFF, cpu.Y);  // Expected value of Y register after decrementing
+
+  cpu.Y = 0x80;                  // Set Y register to 128
+  cpu.ExecuteInstruction(0x88);  // Execute DEY instruction
+  EXPECT_EQ(0x7F, cpu.Y);  // Expected value of Y register after decrementing
+}
+
+// ============================================================================
+// INC - Increment Memory
+
+/**
+TEST_F(CPUTest, INC) {
+  cpu.status &= 0x20;
+
+  EXPECT_CALL(mock_memory, WriteByte(0x1000, 0x7F)).WillOnce(Return());
+  EXPECT_CALL(mock_memory, ReadByte(_)).WillOnce(Return(0x7F));
+  EXPECT_CALL(mock_memory, WriteByte(0x1000, 0x80)).WillOnce(Return());
+
+  cpu.WriteByte(0x1000, 0x7F);
+  cpu.INC(0x1000);
+  EXPECT_EQ(cpu.ReadByte(0x1000), 0x80);
+  EXPECT_TRUE(cpu.GetNegativeFlag());
+  EXPECT_FALSE(cpu.GetZeroFlag());
+
+  EXPECT_CALL(mock_memory, WriteByte(0x1000, 0xFF)).WillOnce(Return());
+  cpu.WriteByte(0x1000, 0xFF);
+  cpu.INC(0x1000);
+  EXPECT_CALL(mock_memory, ReadByte(_)).WillOnce(Return(0x00));
+  EXPECT_EQ(cpu.ReadByte(0x1000), 0x00);
+  EXPECT_FALSE(cpu.GetNegativeFlag());
+  EXPECT_TRUE(cpu.GetZeroFlag());
+}
+*/
+
+TEST_F(CPUTest, INX) {
+  cpu.X = 0x7F;
+  cpu.INX();
+  EXPECT_EQ(cpu.X, 0x80);
+  EXPECT_TRUE(cpu.GetNegativeFlag());
+  EXPECT_FALSE(cpu.GetZeroFlag());
+
+  cpu.X = 0xFF;
+  cpu.INX();
+  EXPECT_EQ(cpu.X, 0x00);
+  EXPECT_FALSE(cpu.GetNegativeFlag());
+  EXPECT_TRUE(cpu.GetZeroFlag());
+}
+
+TEST_F(CPUTest, INY) {
+  cpu.Y = 0x7F;
+  cpu.INY();
+  EXPECT_EQ(cpu.Y, 0x80);
+  EXPECT_TRUE(cpu.GetNegativeFlag());
+  EXPECT_FALSE(cpu.GetZeroFlag());
+
+  cpu.Y = 0xFF;
+  cpu.INY();
+  EXPECT_EQ(cpu.Y, 0x00);
+  EXPECT_FALSE(cpu.GetNegativeFlag());
+  EXPECT_TRUE(cpu.GetZeroFlag());
+}
+
 // ============================================================================
 // Stack Tests
 
@@ -507,6 +664,35 @@ TEST_F(CPUTest, TAY) {
   EXPECT_EQ(cpu.Y, 0xDE);        // Y register should now be equal to A
 }
 
+// ============================================================================
+// XCE - Exchange Carry and Emulation Flags
+
+TEST_F(CPUTest, XCESwitchToNativeMode) {
+  cpu.ExecuteInstruction(0x18);  // Clear carry flag
+  cpu.ExecuteInstruction(0xFB);  // Switch to native mode
+  EXPECT_FALSE(cpu.E);           // Emulation mode flag should be cleared
+}
+
+TEST_F(CPUTest, XCESwitchToEmulationMode) {
+  cpu.ExecuteInstruction(0x38);  // Set carry flag
+  cpu.ExecuteInstruction(0xFB);  // Switch to emulation mode
+  EXPECT_TRUE(cpu.E);            // Emulation mode flag should be set
+}
+
+TEST_F(CPUTest, XCESwitchBackAndForth) {
+  cpu.ExecuteInstruction(0x18);  // Clear carry flag
+  cpu.ExecuteInstruction(0xFB);  // Switch to native mode
+  EXPECT_FALSE(cpu.E);           // Emulation mode flag should be cleared
+
+  cpu.ExecuteInstruction(0x38);  // Set carry flag
+  cpu.ExecuteInstruction(0xFB);  // Switch to emulation mode
+  EXPECT_TRUE(cpu.E);            // Emulation mode flag should be set
+
+  cpu.ExecuteInstruction(0x18);  // Clear carry flag
+  cpu.ExecuteInstruction(0xFB);  // Switch to native mode
+  EXPECT_FALSE(cpu.E);           // Emulation mode flag should be cleared
+}
+
 }  // namespace emu
 }  // namespace app
 }  // namespace yaze