diff --git a/src/py65/devices/mpu65c02.py b/src/py65/devices/mpu65c02.py
index b556d1e..719b380 100644
--- a/src/py65/devices/mpu65c02.py
+++ b/src/py65/devices/mpu65c02.py
@@ -22,6 +22,10 @@ class MPU(NMOS6502):
 
     # instructions
 
+    @instruction(0x5a, 3)
+    def i5a(self):
+        self.stPush(self.y)
+
     @instruction(0x64, 3)
     def i64(self):
         self.opSTZ(self.ZeroPageAddr)
@@ -32,6 +36,11 @@ class MPU(NMOS6502):
         self.opSTZ(self.ZeroPageXAddr)
         self.pc += 1
 
+    @instruction(0x7a, 4)
+    def ifa(self):
+      self.y = self.stPop()
+      self.FlagsNZ(self.y)    
+
     @instruction(0x9c, 4)
     def i9c(self):
         self.opSTZ(self.AbsoluteAddr)
@@ -42,3 +51,11 @@ class MPU(NMOS6502):
         self.opSTZ(self.AbsoluteXAddr)
         self.pc+=2
 
+    @instruction(0xda, 3)
+    def i5a(self):
+        self.stPush(self.x)
+
+    @instruction(0xfa, 4)
+    def ifa(self):
+      self.x = self.stPop()
+      self.FlagsNZ(self.x)     
\ No newline at end of file
diff --git a/src/py65/tests/devices/test_mpu65c02.py b/src/py65/tests/devices/test_mpu65c02.py
index addd4f5..bf7d67a 100644
--- a/src/py65/tests/devices/test_mpu65c02.py
+++ b/src/py65/tests/devices/test_mpu65c02.py
@@ -12,6 +12,60 @@ class MPUTests(unittest.TestCase, Common6502Tests):
         self.assertEquals('<65C02: A=00, X=00, Y=00, Flags=20, SP=ff, PC=0000>',
                           repr(mpu))
 
+    # PHX
+  
+    def test_phx_pushes_x_and_updates_sp(self):
+        mpu = self._make_mpu()
+        mpu.x = 0xAB
+        mpu.memory[0x0000] = 0xDA #=> PHX
+        mpu.step()
+        self.assertEquals(0x0001, mpu.pc)
+        self.assertEquals(0xAB, mpu.x)
+        self.assertEquals(0xAB, mpu.memory[0x01FF])
+        self.assertEquals(0xFE, mpu.sp)
+        self.assertEquals(3, mpu.processorCycles) 
+        
+    # PHY
+  
+    def test_phy_pushes_y_and_updates_sp(self):
+        mpu = self._make_mpu()
+        mpu.y = 0xAB
+        mpu.memory[0x0000] = 0x5A #=> PHY
+        mpu.step()
+        self.assertEquals(0x0001, mpu.pc)
+        self.assertEquals(0xAB, mpu.y)
+        self.assertEquals(0xAB, mpu.memory[0x01FF])
+        self.assertEquals(0xFE, mpu.sp)
+        self.assertEquals(3, mpu.processorCycles)
+
+    # PLX
+    
+    def test_plx_pulls_top_byte_from_stack_into_x_and_updates_sp(self):
+        mpu = self._make_mpu()
+        mpu.memory[0x0000] = 0xFA #=> PLX
+        mpu.memory[0x01FF] = 0xAB
+        mpu.sp = 0xFE
+        mpu.step()
+        self.assertEquals(0x0001, mpu.pc)
+        self.assertEquals(0xAB,   mpu.x)
+        self.assertEquals(0xFF,   mpu.sp)
+        self.assertEquals(4, mpu.processorCycles)
+        
+    # PLY
+    
+    def test_ply_pulls_top_byte_from_stack_into_y_and_updates_sp(self):
+        mpu = self._make_mpu()
+        mpu.memory[0x0000] = 0x7A #=> PLY
+        mpu.memory[0x01FF] = 0xAB
+        mpu.sp = 0xFE
+        mpu.step()
+        self.assertEquals(0x0001, mpu.pc)
+        self.assertEquals(0xAB,   mpu.y)
+        self.assertEquals(0xFF,   mpu.sp)
+        self.assertEquals(4, mpu.processorCycles) 
+        
+    # STZ Zero Page
+
     def test_stz_zp_stores_zero(self):
         mpu = self._make_mpu(debug=True)
         mpu.memory[0x0032] = 0x88
@@ -19,8 +73,49 @@ class MPUTests(unittest.TestCase, Common6502Tests):
         self.assertEquals(0x88, mpu.memory[0x0032])
         mpu.step()
         self.assertEquals(0x00, mpu.memory[0x0032])
+        self.assertEquals(0x0002, mpu.pc)
         self.assertEquals(3, mpu.processorCycles)
 
+    # STZ Zero Page, X-Indexed
+
+    def test_stz_zp_x_stores_zero(self):
+        mpu = self._make_mpu(debug=True)
+        mpu.memory[0x0032] = 0x88
+        mpu.memory[0x0000:0x0000+2] = [0x74, 0x32] #=> STZ $32,X
+        self.assertEquals(0x88, mpu.memory[0x0032])
+        mpu.step()
+        self.assertEquals(0x00, mpu.memory[0x0032])
+        self.assertEquals(0x0002, mpu.pc)
+        self.assertEquals(4, mpu.processorCycles)
+
+    # STZ Absolute
+
+    def test_stz_abs_stores_zero(self):
+        mpu = self._make_mpu(debug=True)
+        mpu.memory[0xFEED] = 0x88
+        mpu.memory[0x0000:0x0000+3] = [0x9C, 0xED, 0xFE] #=> STZ $FEED
+        self.assertEquals(0x88, mpu.memory[0xFEED])
+        mpu.step()
+        self.assertEquals(0x00, mpu.memory[0xFEED])
+        self.assertEquals(0x0003, mpu.pc)
+        self.assertEquals(4, mpu.processorCycles)
+
+    # STZ Absolute, X-Indexed
+
+    def test_stz_abs_stores_zero(self):
+        mpu = self._make_mpu(debug=True)
+        mpu.memory[0xFEED] = 0x88
+        mpu.x = 0x0D
+        mpu.memory[0x0000:0x0000+3] = [0x9E, 0xE0, 0xFE] #=> STZ $FEE0,X
+        self.assertEquals(0x88, mpu.memory[0xFEED])
+        self.assertEquals(0x0D, mpu.x)
+        mpu.step()
+        self.assertEquals(0x00, mpu.memory[0xFEED])
+        self.assertEquals(0x0003, mpu.pc)
+        self.assertEquals(5, mpu.processorCycles)
+ 
+
+
     # Test Helpers
 
     def _get_target_class(self):