diff --git a/cpu.h b/cpu.h
new file mode 100644
index 0000000..bbe6c60
--- /dev/null
+++ b/cpu.h
@@ -0,0 +1,117 @@
+#pragma once
+
+#include <stdint.h>
+
+enum // Registers
+{
+	A, X, Y, SR, SP
+};
+
+enum // Flags
+{
+	CARRY	= 1 << 0,
+	ZERO	= 1 << 1,
+	NO_INT	= 1 << 2,
+	DECIMAL	= 1 << 3,
+	BREAK	= 1 << 4,
+	UNUSED	= 1 << 5,
+	OVERFLW	= 1 << 6,
+	NEGATIV	= 1 << 7,
+};
+
+enum // Address Modes
+{
+	AM_ACC,	// Accumulator implied as operand
+	AM_IMP,	// Implied operand
+	AM_IMM,	// Immediate operand (8 bit)
+	AM_ABS,	// Absolute operand (16 bit)
+	AM_ZP,	// Zero-page operand
+	AM_REL,	// Relative operand (signed 8 bit)
+	AM_IND,	// Absolute indirect operand (16 bit address of 16 bit address)
+	AM_AX,	// Absolute indexed with X
+	AM_AY,	// Absolute indexed with Y
+	AM_ZPX,	// Zero-page indexed with X
+	AM_ZPY,	// Zero-page indexed with Y
+	AM_ZIX,	// Zero-page indexed indirect (zp,x)
+	AM_ZIY,	// Zero-page indirect indexed (zp),y
+};
+
+enum // Opcodes
+{
+	LDA,
+	LDX,
+	LDY,
+	STA,
+	STX,
+	STY,
+	ADC,
+	SBC,
+	INC,
+	INX,
+	INY,
+	DEC,
+	DEX,
+	DEY,
+	ASL,
+	LSR,
+	ROL,
+	ROR,
+	AND,
+	ORA,
+	EOR,
+	CMP,
+	CPX,
+	CPY,
+	BIT,
+	BCC,
+	BCS,
+	BNE,
+	BEQ,
+	BPL,
+	BMI,
+	BVC,
+	BVS,
+	TAX,
+	TXA,
+	TAY,
+	TYA,
+	TSX,
+	TXS,
+	PHA,
+	PLA,
+	PHP,
+	PLP,
+	JMP,
+	JSR,
+	RTS,
+	RTI,
+	CLC,
+	SEC,
+	CLD,
+	SED,
+	CLI,
+	SEI,
+	CLV,
+	BRK,
+	NOP,
+};
+
+// Emulator instance, create with new_cpu()
+typedef struct
+{
+	uint8_t regs[5]; // A, X, Y, SP and SR registers
+	uint16_t pc;
+	uint8_t *mem;
+} cpu_t;
+
+// Argument type, includes both pointer and its value
+typedef struct
+{
+	uint16_t val; // Value at pointer (used by most instructions)
+	uint16_t ptr; // Pointer (used by jumps, etc)
+} arg_t;
+
+cpu_t new_cpu();
+void free_cpu(cpu_t *cpu);
+void die(const char *message);
+void disas(cpu_t *cpu);