Implement LSR (absolute).

hainesr · Oct 24, 2020 · a7afb5d · a7afb5d
1 parent 458cbfb
commit a7afb5d
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diff --git a/lib/mos6502/cpu_instructions.rb b/lib/mos6502/cpu_instructions.rb
@@ -147,6 +147,12 @@ def instructions
           @pc = absolute
         },
 
+        # LSR (absolute)
+        0x4e => lambda {
+          address = absolute
+          @memory.set(address, lsr(@memory.get(address)))
+        },
+
         # BVC
         0x50 => lambda {
           offset = next_byte

diff --git a/test/cpu_instructions_test.rb b/test/cpu_instructions_test.rb
@@ -284,6 +284,17 @@ def test_0x4c
     assert_equal(0x047f, @cpu.pc)
   end
 
+  def test_0x4e
+    @cpu.load!([0xa9, 0x7f, 0x8d, 0x0f, 0x70, 0x4e, 0x0f, 0x70])
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    assert(@cpu.carry?)
+    refute(@cpu.negative?)
+    refute(@cpu.zero?)
+    assert_equal([0x3f], @cpu.dump_memory(0x700f, 1))
+  end
+
   def test_0x50
     @cpu.load!(
       [0xa9, 0x40, 0x48, 0x28, 0x50, 0x03, 0xb8, 0x50, 0xfb, 0xa0, 0xff]