Add support for 65C02 opcode 0x89 (BIT immediate)

CHANGES.txt

@@ -11,6 +11,8 @@
   - Fixed a bug where the MPU status display would wrap unexpectedly
     on some terminals.
 
+  - Added support for 65C02 opcode 0x89 (BIT immediate).
+
 0.13 (2012-11-15)
 
   - Fixed a bug where negative numbers could be entered

py65/devices/mpu65c02.py

@@ -159,6 +159,16 @@ class MPU(mpu6502.MPU):
         self.opSMB(self.ZeroPageAddr, 0x01)
         self.pc += 1
 
+    @instruction(name="BIT", mode="imm", cycles=2)
+    def inst_0x89(self):
+        # This instruction (BIT #$12) does not use opBIT because in the
+        # immediate mode, BIT only affects the Z flag.
+        tbyte = self.ImmediateByte()
+        self.p &= ~(self.ZERO)
+        if (self.a & tbyte) == 0:
+            self.p |= self.ZERO
+        self.pc += 1
+
     @instruction(name="STA", mode="zpi", cycles=5)
     def inst_0x92(self):
         self.opSTA(self.ZeroPageIndirectAddr)

py65/tests/devices/test_mpu65c02.py

@@ -280,6 +280,57 @@ class MPUTests(unittest.TestCase, Common6502Tests):
         self.assertEqual(4, mpu.processorCycles)
         self.assertEqual(0x0003, mpu.pc)
 
+    # BIT (Immediate)
+
+    def test_bit_imm_does_not_affect_n_and_z_flags(self):
+        mpu = self._make_mpu()
+        mpu.p |= mpu.NEGATIVE | mpu.OVERFLOW
+        # $0000 BIT #$FF
+        self._write(mpu.memory, 0x0000, (0x89, 0xff))
+        mpu.a = 0x00
+        mpu.step()
+        self.assertEqual(mpu.NEGATIVE, mpu.p & mpu.NEGATIVE)
+        self.assertEqual(mpu.OVERFLOW, mpu.p & mpu.OVERFLOW)
+        self.assertEqual(0x00, mpu.a)
+        self.assertEqual(2, mpu.processorCycles)
+        self.assertEqual(0x02, mpu.pc)
+
+    def test_bit_imm_stores_result_of_and_in_z_preserves_a_when_1(self):
+        mpu = self._make_mpu()
+        mpu.p &= ~mpu.ZERO
+        # $0000 BIT #$00
+        self._write(mpu.memory, 0x0000, (0x89, 0x00))
+        mpu.a = 0x01
+        mpu.step()
+        self.assertEqual(mpu.ZERO, mpu.p & mpu.ZERO)
+        self.assertEqual(0x01, mpu.a)
+        self.assertEqual(2, mpu.processorCycles)
+        self.assertEqual(0x02, mpu.pc)
+
+    def test_bit_imm_stores_result_of_and_when_nonzero_in_z_preserves_a(self):
+        mpu = self._make_mpu()
+        mpu.p |= mpu.ZERO
+        # $0000 BIT #$01
+        self._write(mpu.memory, 0x0000, (0x89, 0x01))
+        mpu.a = 0x01
+        mpu.step()
+        self.assertEqual(0, mpu.p & mpu.ZERO)  # result of AND is non-zero
+        self.assertEqual(0x01, mpu.a)
+        self.assertEqual(2, mpu.processorCycles)
+        self.assertEqual(0x02, mpu.pc)
+
+    def test_bit_imm_stores_result_of_and_when_zero_in_z_preserves_a(self):
+        mpu = self._make_mpu()
+        mpu.p &= ~(mpu.ZERO)
+        # $0000 BIT #$00
+        self._write(mpu.memory, 0x0000, (0x89, 0x00))
+        mpu.a = 0x01
+        mpu.step()
+        self.assertEqual(mpu.ZERO, mpu.p & mpu.ZERO)  # result of AND is zero
+        self.assertEqual(0x01, mpu.a)
+        self.assertEqual(2, mpu.processorCycles)
+        self.assertEqual(0x02, mpu.pc)
+
     # BIT (Zero Page, X-Indexed)
 
     def test_bit_zp_x_copies_bit_7_of_memory_to_n_flag_when_0(self):