Implement AND (indirect indexed).

hainesr · Oct 25, 2020 · 59b0306 · 59b0306
1 parent 9a65225
commit 59b0306
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diff --git a/lib/mos6502/cpu_instructions.rb b/lib/mos6502/cpu_instructions.rb
@@ -145,6 +145,12 @@ def instructions
           @pc = branch(offset) if @status.negative?
         },
 
+        # AND (indirect indexed)
+        0x31 => lambda {
+          @a &= @memory.get(indirect_indexed)
+          set_nz_flags(@a)
+        },
+
         # AND (zero page, X)
         0x35 => lambda {
           @a &= @memory.get(zero_page(@x))

diff --git a/test/cpu_instructions_test.rb b/test/cpu_instructions_test.rb
@@ -280,6 +280,18 @@ def test_0x30
     assert_equal(0xff, @cpu.y)
   end
 
+  def test_0x31
+    @cpu.load!([0xa2, 0x06, 0x86, 0x76, 0xa0, 0x04, 0xa9, 0x3f, 0x31, 0x75])
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    assert_equal(0x20, @cpu.a)
+    refute(@cpu.negative?)
+    refute(@cpu.zero?)
+  end
+
   def test_0x35
     @cpu.load!([0xa9, 0xb3, 0xa2, 0x12, 0xa0, 0xb3, 0x94, 0x41, 0x35, 0x41])
     @cpu.step