diff --git a/src/main.rs b/src/main.rs
index 08ad611..19ac3f5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,6 @@
 
 
-
+mod tests;
 mod r6502;
 use r6502::{R6502, Flags, Bus};
 
@@ -42,9 +42,11 @@ fn main()
     cpu.clear_flag(Flags::I);
     println!("\nI Flag is: {}", cpu.check_flag(Flags::I));
 
-    // run_simple_or_program(&mut cpu);
+    run_simple_or_program(&mut cpu);
     run_addition_test(&mut cpu);
 
+
+
     println!("\nFinished.");
 }
 
@@ -52,7 +54,7 @@ fn run_addition_test(cpu: &mut R6502)
 {
     println!("\nRunning a simple addition test with no overflow or carry: 8 + 23");
 
-     //////////////////////////////////
+    //////////////////////////////////
     // Setup Bus with program address
     //////////////////////////////////
 
@@ -77,6 +79,11 @@ fn run_addition_test(cpu: &mut R6502)
     bus.write(addr + 2, 0x69); // ADC - Immediate mode
     bus.write(addr + 3, 0x17);  // Argument
 
+    // Store result into memory to also test the STA instruction
+    bus.write(addr + 4, 0x85); // STA - Zero Page mode
+    bus.write(addr + 5, 0x02);  // Argument
+
+
     ////////////////////
     // Run the program!
     ////////////////////
@@ -84,11 +91,14 @@ fn run_addition_test(cpu: &mut R6502)
     // Restart cpu
     cpu.reset(&mut bus);
 
-    // Clock the cpu twice (Clock essentially runs one full instruction)
+    // Clock the cpu to run the program (Clock essentially runs one full instruction)
+    cpu.clock(&mut bus);
     cpu.clock(&mut bus);
     cpu.clock(&mut bus);
 
-    println!("\nProgram result, A register: {}", cpu.a);
+    println!("\nProgram result, A register: {}", cpu.debug_get_reg(r6502::Registers::A));
+    let result = bus.read(0x0002);
+    println!("\nValue at 0x0002: {}", result);
 
 }
 
@@ -132,5 +142,5 @@ fn run_simple_or_program(cpu: &mut R6502)
     cpu.clock(&mut bus);
     cpu.clock(&mut bus);
 
-    println!("\nProgram result, A register: {}", cpu.a);
+    println!("\nProgram result, A register: {}", cpu.debug_get_reg(r6502::Registers::A));
 }
\ No newline at end of file
diff --git a/src/r6502/addressing_modes.rs b/src/r6502/addressing_modes.rs
index ea6f6c0..9358ede 100644
--- a/src/r6502/addressing_modes.rs
+++ b/src/r6502/addressing_modes.rs
@@ -1,5 +1,5 @@
 
-#![allow(dead_code, non_snake_case)]
+#![allow(unused_variables, dead_code, non_snake_case)]
 
 use super::{R6502, Bus};
 
@@ -46,48 +46,82 @@ impl AddressingModes
     // This is also the accumulator mode
     pub fn IMP(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-
+        cpu.working_data = cpu.a as u16;
     }
 
     pub fn IMM(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        cpu.working_data = bus.read(cpu.pc);
+        cpu.working_data = bus.read(cpu.pc) as u16;
         cpu.pc += 1;
     }
 
     pub fn ZP0(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        
+        let working_addr = bus.read(cpu.pc) as u16 & 0x00FF;
+        cpu.pc += 1;
+
+        cpu.working_data = bus.read(working_addr) as u16;
     }
 
     pub fn ZPX(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        
+        let mut working_addr = bus.read(cpu.pc) as u16 & 0x00FF;
+        working_addr += cpu.x as u16;
+        cpu.pc += 1; 
+
+        cpu.working_data = bus.read(working_addr) as u16;
     }
 
     pub fn ZPY(cpu: &mut R6502, bus: &mut dyn Bus)
     {
+        let mut working_addr = bus.read(cpu.pc) as u16 & 0x00FF;
+        working_addr += cpu.y as u16;
+        cpu.pc += 1; 
         
+        cpu.working_data = bus.read(working_addr) as u16;
     }
 
     pub fn REL(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        
+        // NOTE: Not sure if we can use the working_data variable for this.
+        //          if any instruction using this address mode needs extra data read
+        //          then we need another variable to store this address
+        cpu.working_data = bus.read(cpu.pc) as u16;
+        cpu.pc += 1;
     }
 
     pub fn ABS(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        
+        cpu.working_data = bus.read(cpu.pc) as u16;
+        cpu.pc += 1;
+        cpu.working_data |= (bus.read(cpu.pc) as u16) << 8;
+        cpu.pc += 1;
+
+        cpu.working_data = bus.read(cpu.working_data) as u16 & 0x00FF;
     }
 
     pub fn ABX(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        
+        cpu.working_data = bus.read(cpu.pc) as u16;
+        cpu.pc += 1;
+        cpu.working_data |= (bus.read(cpu.pc) as u16) << 8;
+        cpu.pc += 1;
+
+        cpu.working_data += cpu.x as u16;
+
+        cpu.working_data = bus.read(cpu.working_data) as u16 & 0x00FF;
     }
 
     pub fn ABY(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        
+        cpu.working_data = bus.read(cpu.pc) as u16;
+        cpu.pc += 1;
+        cpu.working_data |= (bus.read(cpu.pc) as u16) << 8;
+        cpu.pc += 1;
+
+        cpu.working_data += cpu.y as u16;
+
+        cpu.working_data = bus.read(cpu.working_data) as u16 & 0x00FF;
     }
 
     pub fn IND(cpu: &mut R6502, bus: &mut dyn Bus)
diff --git a/src/r6502/instructions.rs b/src/r6502/instructions.rs
index 033f201..d817881 100644
--- a/src/r6502/instructions.rs
+++ b/src/r6502/instructions.rs
@@ -39,7 +39,8 @@ impl Instructions
     // GROUP ONE
     pub fn ORA(cpu: &mut R6502, _bus: &mut dyn Bus)
     {
-        cpu.a = cpu.a | cpu.working_data;
+        let data = cpu.working_data as u8;
+        cpu.a = cpu.a | data;
         if cpu.a == 0
         {
             cpu.set_flag(Flags::Z);
@@ -53,7 +54,8 @@ impl Instructions
 
     pub fn AND(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        cpu.a = cpu.a & cpu.working_data;
+        let data = cpu.working_data as u8;
+        cpu.a = cpu.a & data;
         if cpu.a == 0
         {
             cpu.set_flag(Flags::Z);
@@ -67,7 +69,8 @@ impl Instructions
 
     pub fn EOR(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        cpu.a = cpu.a ^ cpu.working_data;
+        let data = cpu.working_data as u8;
+        cpu.a = cpu.a ^ data;
         if cpu.a == 0
         {
             cpu.set_flag(Flags::Z);
@@ -85,7 +88,7 @@ impl Instructions
     pub fn ADC(cpu: &mut R6502, bus: &mut dyn Bus)
     {
         // 16 bit addition to capture the carry easier
-        let temp: u16 = cpu.a as u16 + cpu.working_data as u16;
+        let temp: u16 = cpu.a as u16 + cpu.working_data;
 
         if temp > 255
         {
@@ -115,12 +118,13 @@ impl Instructions
 
     pub fn STA(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-
+        bus.write(cpu.working_data, cpu.a);
     }
 
     pub fn LDA(cpu: &mut R6502, bus: &mut dyn Bus)
     {
-        cpu.a = cpu.working_data;
+        let data = cpu.working_data as u8;
+        cpu.a = data;
 
         if cpu.a == 0
         {
diff --git a/src/r6502/mod.rs b/src/r6502/mod.rs
index 141b97f..d93b7c6 100644
--- a/src/r6502/mod.rs
+++ b/src/r6502/mod.rs
@@ -1,5 +1,5 @@
 
-#![allow(dead_code)]
+#![allow(unused_variables, dead_code, non_snake_case)]
 
 mod addressing_modes;
 mod instructions;
@@ -32,9 +32,20 @@ pub enum Flags
     N = (1 << 7),   // Negative Flag
 }
 
+pub enum Registers
+{
+    A,
+    X,
+    Y,
+    PC,
+    SP,
+    STATUS,
+}
+
+#[derive(Clone, Copy, PartialEq)]
 pub struct R6502
 {
-    pub a: u8,      // Accumulator
+    a: u8,      // Accumulator
     x: u8,      // X Register
     y: u8,      // Y Register
 
@@ -45,9 +56,8 @@ pub struct R6502
     cycles: u32, // Track cycles
 
     // Helper Vars
-    working_data: u8,   // value fetched for the ALU
-    addr_abs: u16,
-    addr_rel: u16,
+    working_data: u16,   // value fetched for the ALU
+    // working_addr: u16,
 }
 
 impl R6502
@@ -55,7 +65,38 @@ impl R6502
     // constructor
     pub fn new() -> R6502
     {
-        R6502 { a: 0, x: 0, y: 0, pc: 0, sp: 0, status: 0, cycles: 0, working_data: 0, addr_abs: 0, addr_rel: 0 }
+        R6502 { a: 0, x: 0, y: 0, pc: 0, sp: 0, status: 0, cycles: 0, working_data: 0 }
+    }
+
+    // Debug Access
+    pub fn debug_get_reg(&self, reg: Registers) -> u16
+    {
+        match reg
+        {
+            Registers::A => self.a as u16,
+            Registers::X => self.x as u16,
+            Registers::Y => self.y as u16,
+
+            Registers::PC => self.pc,
+            Registers::SP => self.sp as u16,
+
+            Registers::STATUS => self.status as u16,
+        }
+    }
+
+    pub fn debug_set_reg(&mut self, reg: Registers, value: u16)
+    {
+        match reg
+        {
+            Registers::A => self.a = value as u8,
+            Registers::X => self.x = value as u8,
+            Registers::Y => self.y = value as u8,
+
+            Registers::PC => self.pc = value,
+            Registers::SP => self.sp  = value as u8,
+
+            Registers::STATUS => self.status = value as u8,
+        }
     }
 
     // signals
@@ -90,8 +131,7 @@ impl R6502
 
         // internal helper variables
         self.working_data = 0;
-        self.addr_abs = 0;
-        self.addr_rel = 0;
+        // self.working_addr = 0;
 
         self.cycles = 8;
     }
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
new file mode 100644
index 0000000..aa5eeb2
--- /dev/null
+++ b/src/tests/mod.rs
@@ -0,0 +1,631 @@
+
+#![allow(dead_code, non_snake_case)]
+
+mod test_bus;
+
+
+#[cfg(test)]
+mod instructions 
+{
+    use super::test_bus::RAMBus;
+    use crate::r6502::{R6502, Bus, Registers};
+
+    //////////////////////////////////////////////////////////////////
+    /// ORA     ORA     ORA     ORA
+    ////////////////////////////////////////////////////////////////// 
+
+    #[test]
+    fn ORA_IMM()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // ORA #2
+        bus.write(addr, 0x09); // ORA - Immediate mode
+        bus.write(addr + 1, 0x02);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+        
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x09);
+
+        // Clock the cpu twice (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x0B in the A register?
+        assert_eq!(0x0B, cpu.debug_get_reg(Registers::A));
+
+    }
+
+    #[test]
+    fn ORA_ZP0()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x02 into memory in the zero page
+        bus.write(0x000A, 0x02);
+
+        // ORA #2
+        bus.write(addr, 0x05); // ORA - Zero Page mode
+        bus.write(addr +1, 0x0A);  // Argument (memory address of the value we want to OR with)
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x09);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x0B in the A register?
+        assert_eq!(0x0B, cpu.debug_get_reg(Registers::A));
+
+    }
+
+    #[test]
+    fn ORA_ZPX()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x02 into memory in the zero page
+        bus.write(0x000A, 0x02);
+
+        // ORA #2
+        bus.write(addr, 0x15); // ORA - Zero Page, X mode
+        bus.write(addr + 1, 0x04);  // Argument (memory address of the value we want to OR with)
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::X, 0x06);
+        cpu.debug_set_reg(Registers::A, 0x09);
+
+
+        // Clock the cpu twice (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x0B in the A register?
+        assert_eq!(0x0B, cpu.debug_get_reg(Registers::A));
+
+    }
+
+    #[test]
+    fn ORA_ABS()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x02 into memory in the zero page
+        bus.write(0x010A, 0x02);
+
+        // ORA #2
+        bus.write(addr, 0x0D); // ORA - Absolute mode
+        bus.write(addr + 1, 0x0A);  // Argument (memory address of the value we want to OR with)
+        bus.write(addr + 2, 0x01);  // Argument (memory address of the value we want to OR with)
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        
+        // manually setup the cpu registers
+       // cpu.debug_set_reg(Registers::X, 0x06);
+        cpu.debug_set_reg(Registers::A, 0x09);
+
+
+        // Clock the cpu twice (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x0B in the A register?
+        assert_eq!(0x0B, cpu.debug_get_reg(Registers::A));
+
+    }
+
+    #[test]
+    fn ORA_ABX()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x02 into memory in the zero page
+        bus.write(0x010B, 0x02);
+
+        // ORA #2
+        bus.write(addr, 0x1D); // ORA - Absolute, X mode
+        bus.write(addr + 1, 0x0A);  // Argument (memory address of the value we want to OR with)
+        bus.write(addr + 2, 0x01);  // Argument (memory address of the value we want to OR with)
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::X, 0x01);
+        cpu.debug_set_reg(Registers::A, 0x09);
+
+
+        // Clock the cpu twice (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x0B in the A register?
+        assert_eq!(0x0B, cpu.debug_get_reg(Registers::A));
+
+    }
+   
+    #[test]
+    fn ORA_ABY()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x02 into memory in the zero page
+        bus.write(0x010B, 0x02);
+
+        // ORA #2
+        bus.write(addr, 0x19); // ORA - Absolute, X mode
+        bus.write(addr + 1, 0x0A);  // Argument (memory address of the value we want to OR with)
+        bus.write(addr + 2, 0x01);  // Argument (memory address of the value we want to OR with)
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::Y, 0x01);
+        cpu.debug_set_reg(Registers::A, 0x09);
+
+
+        // Clock the cpu twice (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x0B in the A register?
+        assert_eq!(0x0B, cpu.debug_get_reg(Registers::A));
+
+    }
+
+    //////////////////////////////////////////////////////////////////
+    /// AND     AND     AND     AND
+    ////////////////////////////////////////////////////////////////// 
+
+    #[test]
+    fn AND_IMM()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // AND #3
+        bus.write(addr, 0x29); // AND - Immediate mode
+        bus.write(addr + 1, 0x03);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x0A);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x02 in the A register?
+        assert_eq!(0x02, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn AND_ZP0()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x0A into memory in the zero page
+        bus.write(0x000B, 0x03);
+
+        // AND #3
+        bus.write(addr, 0x25); // AND - Zero Page mode
+        bus.write(addr + 1, 0x0B);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x0A);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x02 in the A register?
+        assert_eq!(0x02, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn AND_ZPX()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x0A into memory in the zero page
+        bus.write(0x000B, 0x03);
+
+        // AND #3
+        bus.write(addr, 0x35); // AND - Zero Page, X mode
+        bus.write(addr + 1, 0x0A);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x0A);
+        cpu.debug_set_reg(Registers::X, 0x01);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x02 in the A register?
+        assert_eq!(0x02, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn AND_ABS()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x0A into memory in the zero page
+        bus.write(0x010B, 0x03);
+
+        // AND #3
+        bus.write(addr, 0x2D); // AND - Absolute mode
+        bus.write(addr + 1, 0x0B);  // Argument
+        bus.write(addr + 2, 0x01);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x0A);
+        //cpu.debug_set_reg(Registers::X, 0x01);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x02 in the A register?
+        assert_eq!(0x02, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn AND_ABX()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x0A into memory in the zero page
+        bus.write(0x010C, 0x03);
+
+        // AND #3
+        bus.write(addr, 0x3D); // AND - Absolute, X mode
+        bus.write(addr + 1, 0x0B);  // Argument
+        bus.write(addr + 2, 0x01);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x0A);
+        cpu.debug_set_reg(Registers::X, 0x01);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x02 in the A register?
+        assert_eq!(0x02, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn AND_ABY()
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Manually put 0x0A into memory in the zero page
+        bus.write(0x010C, 0x03);
+
+        // AND #3
+        bus.write(addr, 0x39); // AND - Absolute, X mode
+        bus.write(addr + 1, 0x0B);  // Argument
+        bus.write(addr + 2, 0x01);  // Argument
+
+        // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::A, 0x0A);
+        cpu.debug_set_reg(Registers::Y, 0x01);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x02 in the A register?
+        assert_eq!(0x02, cpu.debug_get_reg(Registers::A));
+    }
+
+    //////////////////////////////////////////////////////////////////
+    /// LDA     LDA     LDA     LDA
+    ////////////////////////////////////////////////////////////////// 
+
+    #[test]
+    fn LDA_IMM() 
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+
+        // Program to load 0x08 into the accumulator
+        bus.write(addr, 0xA9); // LDA - Immediate mode
+        bus.write(addr + 1, 0x08);  // Argument
+
+         // Restart cpu
+        cpu.reset(&mut bus);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x08 in the A register?
+        assert_eq!(0x08, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn LDA_ZP0() 
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+  
+        // Manually put 0x08 into memory in the zero page
+        bus.write(0x000A, 0x08);
+
+        // Program to load 0x08 into the accumulator
+        bus.write(addr, 0xA5); // LDA - Zero Page mode
+        bus.write(addr + 1, 0x0A);  // Argument
+
+         // Restart cpu
+        cpu.reset(&mut bus);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x08 in the A register?
+        assert_eq!(0x08, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn LDA_ZPX() 
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+  
+        // Manually put 0x08 into memory in the zero page
+        bus.write(0x000A, 0x08);
+
+        // Program to load 0x08 into the accumulator
+        bus.write(addr, 0xB5); // LDA - Zero Page, X mode
+        bus.write(addr + 1, 0x04);  // Argument
+
+         // Restart cpu
+        cpu.reset(&mut bus);
+
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::X, 0x06);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x08 in the A register?
+        assert_eq!(0x08, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn LDA_ABS() 
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+  
+        // Manually put 0x08 into memory in the zero page
+        bus.write(0x010A, 0x08);
+
+        // Program to load 0x08 into the accumulator
+        bus.write(addr, 0xAD); // LDA - Absolute mode
+        bus.write(addr + 1, 0x0A);  // Argument lo word
+        bus.write(addr + 2, 0x01);  // Argument hi word
+
+         // Restart cpu
+        cpu.reset(&mut bus);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x08 in the A register?
+        assert_eq!(0x08, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn LDA_ABX() 
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+  
+        // Manually put 0x08 into memory in the zero page
+        bus.write(0x010B, 0x08);
+
+        // Program to load 0x08 into the accumulator
+        bus.write(addr, 0xBD); // LDA - Absolute, X mode
+        bus.write(addr + 1, 0x0A);  // Argument lo word
+        bus.write(addr + 2, 0x01);  // Argument hi word
+
+         // Restart cpu
+        cpu.reset(&mut bus);
+        
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::X, 0x01);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x08 in the A register?
+        assert_eq!(0x08, cpu.debug_get_reg(Registers::A));
+    }
+
+    #[test]
+    fn LDA_ABY() 
+    {
+        let mut cpu = R6502::new();
+        let mut bus = RAMBus::new();
+
+        // program address
+        let addr = 0x0020 as u16;
+
+        // Set the program counter address
+        bus.write(0xFFFC, (addr & 0x00FF) as u8);  // low byte
+        bus.write(0xFFFD, ((addr & 0xFF00) >> 8) as u8);  // high byte
+  
+        // Manually put 0x08 into memory in the zero page
+        bus.write(0x010B, 0x08);
+
+        // Program to load 0x08 into the accumulator
+        bus.write(addr, 0xB9); // LDA - Absolute, X mode
+        bus.write(addr + 1, 0x0A);  // Argument lo word
+        bus.write(addr + 2, 0x01);  // Argument hi word
+
+         // Restart cpu
+        cpu.reset(&mut bus);
+        
+        // manually setup the cpu registers
+        cpu.debug_set_reg(Registers::Y, 0x01);
+
+        // Clock the cpu to run the program (Clock essentially runs one full instruction)
+        cpu.clock(&mut bus);
+
+        // Is 0x08 in the A register?
+        assert_eq!(0x08, cpu.debug_get_reg(Registers::A));
+    }
+}
\ No newline at end of file
diff --git a/src/tests/test_bus.rs b/src/tests/test_bus.rs
new file mode 100644
index 0000000..91ac7b2
--- /dev/null
+++ b/src/tests/test_bus.rs
@@ -0,0 +1,28 @@
+use crate::r6502::Bus;
+
+// All-RAM bus for testing
+pub struct RAMBus
+{
+    ram: [u8; 64 * 1024]
+}
+
+impl RAMBus
+{
+    pub fn new() -> RAMBus
+    {
+        RAMBus { ram: [0; 64 * 1024] }
+    }
+}
+
+impl Bus for RAMBus
+{
+    fn read(&self, addr: u16) -> u8 
+    {
+        self.ram[addr as usize]    
+    }
+
+    fn write(&mut self, addr: u16, value: u8) 
+    {
+        self.ram[addr as usize] = value;    
+    }
+}
\ No newline at end of file
diff --git a/todo/todo.todo b/todo/todo.todo
index d725a28..af79cc8 100644
--- a/todo/todo.todo
+++ b/todo/todo.todo
@@ -1,19 +1,29 @@
 
 General:
+    ✔ Add unit tests for each instruction and address mode @done(23-11-07 19:57)
     ☐ Fully implement clock cycle tracking
     ☐ Add a disassembler for debugging
         ☐ Debug data lookup for instructions
 
+CPU:
+    Signals:
+        ✔ Clock @done(23-11-07 20:45)
+        ✔ Reset @done(23-11-07 20:46)
+        ☐ irq function
+        ☐ nmi function
+
 Addressing modes:
-    ☐ IMP - Implied
+    ✔ IMP - Implied @done(23-11-07 14:01)
     ✔ IMM - Immediate @done(23-11-06 19:01)
-    ☐ ZP0 - Zero Page
-    ☐ ZPX - Zero Page, X
-    ☐ ZPY - Zero Page, Y
+    ✔ ZP0 - Zero Page @done(23-11-07 14:40)
+    ✔ ZPX - Zero Page, X @done(23-11-07 14:40)
+    ✔ ZPY - Zero Page, Y @done(23-11-07 14:40)
     ☐ REL - Relative
-    ☐ ABS - Absolute
-    ☐ ABX - Absolute, X
-    ☐ ABY - Absolute, Y
+        ✔ Code @done(23-11-07 20:44)
+        ☐ Test
+    ✔ ABS - Absolute @done(23-11-07 20:25)
+    ✔ ABX - Absolute, X @done(23-11-07 20:25)
+    ✔ ABY - Absolute, Y @done(23-11-07 20:25)
     ☐ IND - Indirect
     ☐ IZX - Indirect, X
     ☐ IZY - Indirect, Y
@@ -21,10 +31,10 @@ Addressing modes:
 Instructions:
     GROUP ONE:
         ✔ 000	ORA @done(23-11-06 18:55)
-        ☐ 001	AND
-        ☐ 010	EOR
-        ☐ 011	ADC
-        ☐ 100	STA
+        ✔ 001	AND @done(23-11-07 13:43)
+        ✔ 010	EOR @done(23-11-07 13:43)
+        ✔ 011	ADC @done(23-11-06 19:59)
+        ✔ 100	STA @done(23-11-07 15:04)
         ✔ 101	LDA @done(23-11-06 18:55)
         ☐ 110	CMP
         ☐ 111	SBC