diff --git a/bin/emu b/bin/emu
deleted file mode 100755
index 0157dea..0000000
Binary files a/bin/emu and /dev/null differ
diff --git a/src/cpu/op.c b/src/cpu/op.c
index b10ebc6..5b948f4 100644
--- a/src/cpu/op.c
+++ b/src/cpu/op.c
@@ -1,26 +1,83 @@
 #include "op.h"
 
-#define IS_ALU_OP_CODE_(op, offset) \
-    case op + offset: \
-        op_##op(); \
+// Reference: https://www.nesdev.org/wiki/CPU_unofficial_opcodes
+
+#define IS_OP_CODE_MODE(op, op_code, addr_mode) \
+    case op_code: \
+        op_ ## op(ADDR_MODE_ ## addr_mode); \
         break;
 
+#define IS_OP_CODE(op, op_code) \
+    IS_OP_CODE_MODE(op, op_code, IMPLICIT)
+
+#define IS_ALU_OP_CODE_(op, offset, addr_mode) \
+    IS_OP_CODE_MODE(op, OP_CODE_ ## op + offset, addr_mode)
+
 #define IS_ALU_OP_CODE(op) \
-    IS_ALU_OP_CODE_(op, 0x01) \
-    IS_ALU_OP_CODE_(op, 0x05) \
-    IS_ALU_OP_CODE_(op, 0x09) \
-    IS_ALU_OP_CODE_(op, 0x0d) \
-    IS_ALU_OP_CODE_(op, 0x11) \
-    IS_ALU_OP_CODE_(op, 0x15) \
-    IS_ALU_OP_CODE_(op, 0x19) \
-    IS_ALU_OP_CODE_(op, 0x1d)
+    IS_ALU_OP_CODE_(op, 0x01, INDEXED_INDIRECT) \
+    IS_ALU_OP_CODE_(op, 0x05, ZERO_PAGE) \
+    IS_ALU_OP_CODE_(op, 0x09, IMMEDIATE) \
+    IS_ALU_OP_CODE_(op, 0x0d, ABSOLUTE) \
+    IS_ALU_OP_CODE_(op, 0x11, INDIRECT_INDEXED) \
+    IS_ALU_OP_CODE_(op, 0x15, ZERO_PAGE_INDEXED_X) \
+    IS_ALU_OP_CODE_(op, 0x19, ABSOLUTE_INDEXED_Y) \
+    IS_ALU_OP_CODE_(op, 0x1d, ABSOLUTE_INDEXED_X)
+
+#define IS_ALU_OP_CODE_NO_IMMEDIATE(op) \
+    IS_ALU_OP_CODE_(op, 0x01, INDEXED_INDIRECT) \
+    IS_ALU_OP_CODE_(op, 0x05, ZERO_PAGE) \
+    IS_ALU_OP_CODE_(op, 0x0d, ABSOLUTE) \
+    IS_ALU_OP_CODE_(op, 0x11, INDIRECT_INDEXED) \
+    IS_ALU_OP_CODE_(op, 0x15, ZERO_PAGE_INDEXED_X) \
+    IS_ALU_OP_CODE_(op, 0x19, ABSOLUTE_INDEXED_Y) \
+    IS_ALU_OP_CODE_(op, 0x1d, ABSOLUTE_INDEXED_X)
+
+void op_ORA(addr_mode_t addr_mode) {
+
+}
+
+void op_AND(addr_mode_t addr_mode) {
+
+}
+
+void op_EOR(addr_mode_t addr_mode) {
+
+}
+
+void op_ADC(addr_mode_t addr_mode) {
+
+}
+
+void op_STA(addr_mode_t addr_mode) {
+
+}
+
+void op_LDA(addr_mode_t addr_mode) {
+
+}
+
+void op_CMP(addr_mode_t addr_mode) {
+
+}
+
+void op_SBC(addr_mode_t addr_mode) {
+
+}
 
 void process_op_code(int op) {
     switch (op) {
-    IS_ALU_OP_CODE(AND)
+        // CTRL
+        IS_OP_CODE(BRK, 0x00)
+        IS_OP_CODE_MODE(NOP, 0x04, ZERO_PAGE)
+
+        // ALU
+        IS_ALU_OP_CODE(ORA)
+        IS_ALU_OP_CODE(AND)
+        IS_ALU_OP_CODE(EOR)
+        IS_ALU_OP_CODE(ADC)
+        IS_ALU_OP_CODE_NO_IMMEDIATE(STA)
+        IS_ALU_OP_CODE(LDA)
+        IS_ALU_OP_CODE(CMP)
+        IS_ALU_OP_CODE(SBC)
     }
 }
-
-void op_AND() {
-
-}
diff --git a/src/cpu/op.h b/src/cpu/op.h
index c8f08a4..538c049 100644
--- a/src/cpu/op.h
+++ b/src/cpu/op.h
@@ -1,10 +1,34 @@
+#ifndef CPU_OP_H
+#define CPU_OP_H
+
+// The number associated with each op code is the matching line of the ALU op code.
+// Based on the table here: https://www.nesdev.org/wiki/CPU_unofficial_opcodes
 enum op_code {
-    ORA = 0x00,
-    AND = 0x20,
-    EOR = 0x40,
-    ADC = 0x60,
-    STA = 0x80,
-    LDA = 0xa0,
-    CMP = 0xc0,
-    SBC = 0xe0
+    OP_CODE_ORA = 0x00,
+    OP_CODE_AND = 0x20,
+    OP_CODE_EOR = 0x40,
+    OP_CODE_ADC = 0x60,
+    OP_CODE_STA = 0x80,
+    OP_CODE_LDA = 0xa0,
+    OP_CODE_CMP = 0xc0,
+    OP_CODE_SBC = 0xe0
 };
+
+typedef enum {
+    ADDR_MODE_ABSOLUTE,             // a
+    ADDR_MODE_ABSOLUTE_JUMP,        // (a)
+    ADDR_MODE_ABSOLUTE_INDEXED_X,   // a,x
+    ADDR_MODE_ABSOLUTE_INDEXED_Y,   // a,y
+    ADDR_MODE_ACCUMULATOR,          // A
+    ADDR_MODE_IMMEDIATE,            // #i
+    ADDR_MODE_IMPLICIT,             // Imp
+    ADDR_MODE_INDEXED_INDIRECT,     // (d,x)
+    ADDR_MODE_INDIRECT_JUMP,        //
+    ADDR_MODE_INDIRECT_INDEXED,     // (d),y
+    ADDR_MODE_RELATIVE,             // label
+    ADDR_MODE_ZERO_PAGE,            // d
+    ADDR_MODE_ZERO_PAGE_INDEXED_X,  // d,x
+    ADDR_MODE_ZERO_PAGE_INDEXED_Y,  // d,y
+} addr_mode_t;
+
+#endif