diff --git a/src/arm7tdmi/arm/exec.rs b/src/arm7tdmi/arm/exec.rs
index 8427968..701127f 100644
--- a/src/arm7tdmi/arm/exec.rs
+++ b/src/arm7tdmi/arm/exec.rs
@@ -162,7 +162,7 @@ impl Core {
         res
     }
 
-    fn alu(&mut self, opcode: ArmOpCode, op1: i32, op2: i32, set_cond_flags: bool) -> Option<i32> {
+    pub fn alu(&mut self, opcode: ArmOpCode, op1: i32, op2: i32, set_cond_flags: bool) -> Option<i32> {
         let C = self.cpsr.C() as i32;
 
         let mut carry = self.cpsr.C();
diff --git a/src/arm7tdmi/mod.rs b/src/arm7tdmi/mod.rs
index a42d491..9ffc6ea 100644
--- a/src/arm7tdmi/mod.rs
+++ b/src/arm7tdmi/mod.rs
@@ -39,7 +39,7 @@ impl fmt::Display for DecodedInstruction {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
             DecodedInstruction::Arm(a) => write!(f, "{}", a),
-            DecodedInstruction::Thumb(t) => write!(f, "{:#?}", t),
+            DecodedInstruction::Thumb(t) => write!(f, "{}", t),
         }
     }
 }
diff --git a/src/arm7tdmi/thumb/display.rs b/src/arm7tdmi/thumb/display.rs
index 1eed6e3..875bece 100644
--- a/src/arm7tdmi/thumb/display.rs
+++ b/src/arm7tdmi/thumb/display.rs
@@ -20,7 +20,7 @@ impl ThumbInstruction {
     fn fmt_data_process_imm(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(
             f,
-            "{op}\t{Rd}, #{Offset8}",
+            "{op}\t{Rd}, #{Offset8:#x}",
             op = self.format3_op(),
             Rd = reg_string(self.rd()),
             Offset8 = self.offset8()
diff --git a/src/arm7tdmi/thumb/exec.rs b/src/arm7tdmi/thumb/exec.rs
index bbfe2ff..d24f77f 100644
--- a/src/arm7tdmi/thumb/exec.rs
+++ b/src/arm7tdmi/thumb/exec.rs
@@ -1,9 +1,36 @@
-use super::super::cpu::{Core, CpuExecResult};
-use super::ThumbInstruction;
-use crate::arm7tdmi::bus::Bus;
+use crate::arm7tdmi::arm::exec::*;
+use crate::arm7tdmi::arm::ArmOpCode;
+use crate::arm7tdmi::bus::{Bus, MemoryAccessType::*, MemoryAccessWidth::*};
+use crate::arm7tdmi::cpu::{Core, CpuExecResult, CpuPipelineAction};
+
+use super::{ThumbFormat, ThumbInstruction};
 
 impl Core {
+    fn exec_thumb_data_process_imm(
+        &mut self,
+        sysbus: &mut Bus,
+        insn: ThumbInstruction,
+    ) -> CpuExecResult {
+        let arm_alu_op: ArmOpCode = insn.format3_op().into();
+        let op1 = self.get_reg(insn.rd()) as i32;
+        let op2 = insn.offset8() as i32;
+        let result = self.alu(arm_alu_op, op1, op2, true);
+        if let Some(result) = result {
+            self.set_reg(insn.rd(), result as u32);
+        }
+        // +1S
+        self.add_cycles(
+            self.pc + (self.word_size() as u32),
+            sysbus,
+            Seq + MemoryAccess32,
+        );
+        Ok(CpuPipelineAction::IncPC)
+    }
+
     pub fn exec_thumb(&mut self, sysbus: &mut Bus, insn: ThumbInstruction) -> CpuExecResult {
-        unimplemented!("thumb not implemented {:#}", insn)
+        match insn.fmt {
+            ThumbFormat::DataProcessImm => self.exec_thumb_data_process_imm(sysbus, insn),
+            _ => unimplemented!("thumb not implemented {:#}", insn),
+        }
     }
 }
diff --git a/src/arm7tdmi/thumb/mod.rs b/src/arm7tdmi/thumb/mod.rs
index 2ab3905..81f45be 100644
--- a/src/arm7tdmi/thumb/mod.rs
+++ b/src/arm7tdmi/thumb/mod.rs
@@ -4,7 +4,7 @@ use crate::bit::BitIndex;
 use crate::byteorder::{LittleEndian, ReadBytesExt};
 use crate::num::FromPrimitive;
 
-use super::arm::{ArmCond, ArmShiftType};
+use super::arm::{ArmCond, ArmOpCode, ArmShiftType};
 use super::{Addr, InstructionDecoder, InstructionDecoderError};
 
 pub mod display;
@@ -159,6 +159,17 @@ pub enum OpFormat3 {
     SUB = 3,
 }
 
+impl From<OpFormat3> for ArmOpCode {
+    fn from(op: OpFormat3) -> ArmOpCode {
+        match op {
+            OpFormat3::MOV => ArmOpCode::MOV,
+            OpFormat3::CMP => ArmOpCode::CMP,
+            OpFormat3::ADD => ArmOpCode::ADD,
+            OpFormat3::SUB => ArmOpCode::SUB,
+        }
+    }
+}
+
 #[derive(Debug, Primitive)]
 pub enum OpFormat5 {
     ADD = 0,
@@ -167,12 +178,29 @@ pub enum OpFormat5 {
     BX = 3,
 }
 
+impl From<OpFormat5> for ArmOpCode {
+    fn from(op: OpFormat5) -> ArmOpCode {
+        match op {
+            OpFormat5::ADD => ArmOpCode::ADD,
+            OpFormat5::CMP => ArmOpCode::CMP,
+            OpFormat5::MOV => ArmOpCode::MOV,
+            _ => unreachable!(), // this should not be called if op = BX
+        }
+    }
+}
+
 impl ThumbInstruction {
     const FLAG_H1: usize = 7;
     const FLAG_H2: usize = 6;
 
     pub fn rd(&self) -> usize {
-        (self.raw & 0b111) as usize
+        match self.fmt {
+            ThumbFormat::DataProcessImm
+            | ThumbFormat::LdrPc
+            | ThumbFormat::LdrStrSp
+            | ThumbFormat::LdrAddress => self.raw.bit_range(8..11) as usize,
+            _ => (self.raw & 0b111) as usize,
+        }
     }
 
     pub fn rs(&self) -> usize {
@@ -239,3 +267,30 @@ impl ThumbInstruction {
         self.raw.bit(bit)
     }
 }
+
+#[cfg(test)]
+/// All instructions constants were generated using an ARM assembler.
+mod tests {
+    use super::*;
+
+    #[test]
+    fn mov_low_reg() {
+        use crate::arm7tdmi::cpu::{Core, CpuPipelineAction};
+        use crate::sysbus::BoxedMemory;
+
+        let bytes = vec![];
+        let mut mem = BoxedMemory::new(bytes.into_boxed_slice());
+        let mut core = Core::new();
+        core.set_reg(0, 0);
+
+        // movs r0, #0x27
+        let insn = ThumbInstruction::decode(0x2027, 0).unwrap();
+
+        assert_eq!(format!("{}", insn), "mov\tr0, #0x27");
+        assert_eq!(
+            core.exec_thumb(&mut mem, insn),
+            Ok(CpuPipelineAction::IncPC)
+        );
+        assert_eq!(core.get_reg(0), 0x27);
+    }
+}
diff --git a/src/sysbus.rs b/src/sysbus.rs
index 00dc3b8..7e958cb 100644
--- a/src/sysbus.rs
+++ b/src/sysbus.rs
@@ -10,13 +10,23 @@ const PALETTE_RAM_SIZE: usize = 1 * 1024;
 const OAM_SIZE: usize = 1 * 1024;
 
 #[derive(Debug)]
-struct BoxedMemory(Box<[u8]>, WaitState);
+pub struct BoxedMemory(Box<[u8]>, WaitState);
+
+impl BoxedMemory {
+    pub fn new(boxed_slice: Box<[u8]>) -> BoxedMemory {
+        BoxedMemory(boxed_slice, Default::default())
+    }
+
+    pub fn new_with_waitstate(boxed_slice: Box<[u8]>, ws: WaitState) -> BoxedMemory {
+        BoxedMemory(boxed_slice, ws)
+    }
+}
 
 #[derive(Debug)]
-struct WaitState {
-    access8: usize,
-    access16: usize,
-    access32: usize,
+pub struct WaitState {
+    pub access8: usize,
+    pub access16: usize,
+    pub access32: usize,
 }
 
 impl WaitState {