diff --git a/src/arm7tdmi.rs b/src/arm7tdmi.rs
index 138a2e7b..527aec61 100644
--- a/src/arm7tdmi.rs
+++ b/src/arm7tdmi.rs
@@ -3,6 +3,8 @@ use std::convert::TryInto;
 use crate::alu_instruction::ArmModeAluInstruction;
 use crate::bitwise::Bits;
 use crate::instruction::ArmModeInstruction;
+use crate::internal_memory::InternalMemory;
+use crate::io_device::IoDevice;
 use crate::{condition::Condition, cpsr::Cpsr, cpu::Cpu};
 
 /// Contains the 16 registers for the CPU, latest (R15) is special because
@@ -39,6 +41,8 @@ pub struct Arm7tdmi {
 
     registers: Registers,
     cpsr: Cpsr,
+
+    memory: InternalMemory,
 }
 
 const OPCODE_ARM_SIZE: usize = 4;
@@ -113,6 +117,7 @@ impl Arm7tdmi {
             rom,
             registers: Registers::default(),
             cpsr: Cpsr::default(),
+            memory: InternalMemory::new(),
         }
     }
 
@@ -225,15 +230,20 @@ impl Arm7tdmi {
         let load_store: SingleDataTransfer =
             opcode.try_into().expect("convert to Single Data Transfer");
 
+        let value: u32 = self
+            .memory
+            .read_at(if up_down {
+                address.wrapping_sub(offset)
+            } else {
+                address.wrapping_add(offset)
+            })
+            .try_into()
+            .unwrap(); // FIXME: is this right? Or we should read a WORD (u32)
+
         match load_store {
-            SingleDataTransfer::Ldr => self.registers.set_register_at(
-                rd.try_into().unwrap(),
-                if up_down {
-                    address.wrapping_sub(offset)
-                } else {
-                    address.wrapping_add(offset)
-                },
-            ),
+            SingleDataTransfer::Ldr => self
+                .registers
+                .set_register_at(rd.try_into().unwrap(), value),
             _ => todo!(),
         }
     }
@@ -428,8 +438,11 @@ mod tests {
         // then will be 92 + 8 (.wrapping_sub(offset))
         cpu.registers.set_program_counter(92);
 
+        // simulate mem already contains something.
+        cpu.memory.write_at(76, 99);
+
         cpu.execute(op_code, instruction);
-        assert_eq!(cpu.registers.register_at(13), 76);
+        assert_eq!(cpu.registers.register_at(13), 99);
         assert_eq!(cpu.registers.program_counter(), 96);
     }
 }
diff --git a/src/bitwise.rs b/src/bitwise.rs
index 467413e6..96f6f362 100644
--- a/src/bitwise.rs
+++ b/src/bitwise.rs
@@ -12,6 +12,7 @@ pub trait Bits {
     fn get_bit(self, bit_idx: u8) -> bool;
     fn get_bits(self, bits_range: RangeInclusive<u8>) -> u32;
     fn are_bits_on(self, bits_range: RangeInclusive<u8>) -> bool;
+    fn clear_bits(&mut self, bit_idx: u8, to: u8);
 }
 
 impl Bits for u32 {
@@ -82,6 +83,14 @@ impl Bits for u32 {
         }
         true
     }
+
+    /// To clear all bits from the `from` through `to` (inclusive)
+    fn clear_bits(&mut self, from: u8, to: u8) {
+        let from_mask = (1 << from) - 1;
+        let to_mask = (1 << to) - 1;
+        let mask = !(from_mask - to_mask);
+        *self &= mask;
+    }
 }
 
 #[cfg(test)]
@@ -89,6 +98,22 @@ mod tests {
     use super::*;
     use rand::Rng;
 
+    #[test]
+    fn test_clear_bits_msb_to_idx() {
+        let mut b = 0b11111111;
+        b.clear_bits(5, 2);
+        println!("{}", b);
+        assert_eq!(b, 0b11100011);
+    }
+
+    #[test]
+    fn test_clear_bits_idx_to_0() {
+        let mut b = 0b11111111;
+        b.clear_bits(3, 1);
+        println!("{}", b);
+        assert_eq!(b, 0b11111001);
+    }
+
     #[test]
     fn test_is_on() {
         let b = 0b110011101_u32;
diff --git a/src/internal_memory.rs b/src/internal_memory.rs
index cd9df192..81d3b663 100644
--- a/src/internal_memory.rs
+++ b/src/internal_memory.rs
@@ -6,7 +6,7 @@ pub struct InternalMemory {
 }
 
 impl InternalMemory {
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self {
             internal_work_ram: [0; 0x7FFF],
         }
diff --git a/src/main.rs b/src/main.rs
index 7757ffd7..4867ad68 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,6 +18,8 @@ mod cpsr;
 mod cpu;
 mod egui_app;
 mod instruction;
+mod internal_memory;
+mod io_device;
 mod ppu;
 
 fn main() {