diff --git a/sim/log.log b/sim/log.log
new file mode 100644
index 0000000..d45904e
--- /dev/null
+++ b/sim/log.log
@@ -0,0 +1,120 @@
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B
+a: 000000
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000000
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B
+a: 00002A
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000003
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B
+a: 000045
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000006
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B000045
+a: 000045
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000009
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B000045
+a: 00002A
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 00000C
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B000045
+a: 00000F
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 00000F
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B00004500000F
+a: 00000F
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000012
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B00004500000F
+a: 00002A
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000015
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B00004500000F
+a: 00046E
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000018
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B00004500000F00046E
+a: 00046E
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 00001B
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B00004500000F00046E
+a: 00002A
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 00001E
+sw: 000000
+0320361B20360F203603202D1F202D0F20300320242320240F202A03201B27201B0F20242320150F202103200C1F201B0F20180F20033F2FFD00002A00001B00004500000F00046E
+a: 000001
+x: 000000
+l: 000000
+b: 000000
+s: 000000
+t: 000000
+f: 000000
+pc: 000021
+sw: 000000
diff --git a/sim/src/sim.gleam b/sim/src/sim.gleam
index 00ce928..382372c 100644
--- a/sim/src/sim.gleam
+++ b/sim/src/sim.gleam
@@ -20,13 +20,34 @@ fn step(
   machine
 }
 
+fn status(machine: machine.Machine) {
+  io.println(machine.state_string(machine))
+}
+
 pub fn main() -> Nil {
   let machine = machine.init("../arith.obj")
   let instructions = machine.get_instructions()
-  io.println(machine.state_string(machine))
+  status(machine)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
+  let machine = step(machine, instructions)
   let machine = run_for(machine, instructions, 16)
-  let machine = step(machine, instructions)
-  let machine = step(machine, instructions)
-  let machine = step(machine, instructions)
   Nil
 }
diff --git a/sim/src/sim/device.gleam b/sim/src/sim/device.gleam
new file mode 100644
index 0000000..6984ce2
--- /dev/null
+++ b/sim/src/sim/device.gleam
@@ -0,0 +1,84 @@
+import file_streams/file_open_mode
+import file_streams/file_stream
+import gleam/bit_array
+import gleam/io
+import gleam/option
+
+pub opaque type DeviceType {
+  Stdin
+  Stdout
+  Stderr
+  Default
+}
+
+pub type Device {
+  Device(
+    stream: option.Option(file_stream.FileStream),
+    dev_type: DeviceType,
+    buffer: BitArray,
+    has_data: Bool,
+  )
+}
+
+pub fn open(name: String) -> Device {
+  case name {
+    "0.dev" -> Device(option.None, Stdin, <<>>, False)
+    "1.dev" -> Device(option.None, Stdout, <<>>, False)
+    "2.dev" -> Device(option.None, Stderr, <<>>, False)
+    _ -> {
+      let assert Ok(str) =
+        file_stream.open(name, [file_open_mode.Read, file_open_mode.Write])
+      Device(option.Some(str), Default, <<>>, False)
+    }
+  }
+}
+
+pub fn read(device: Device) -> #(BitArray, Device) {
+  #(device.buffer, Device(..device, buffer: <<>>, has_data: False))
+}
+
+pub fn write(device: Device, char: BitArray) -> Device {
+  let _ = case device.dev_type {
+    Default -> {
+      let assert option.Some(stream) = device.stream
+      let assert Ok(_r) = file_stream.write_bytes(stream, char)
+      let assert Ok(_r) = file_stream.sync(stream)
+      Nil
+    }
+    Stdout -> {
+      let assert Ok(str) = bit_array.to_string(char)
+      io.print(str)
+    }
+    Stderr -> {
+      let assert Ok(str) = bit_array.to_string(char)
+      io.print_error(str)
+    }
+    _ -> Nil
+  }
+  device
+}
+
+pub fn test_device(device: Device) -> Device {
+  case device.dev_type {
+    Default -> {
+      let assert option.Some(stream) = device.stream
+      let data = file_stream.read_bytes(stream, 1)
+      case data {
+        Ok(char) -> Device(..device, buffer: char, has_data: True)
+        Error(_) -> Device(..device, buffer: <<>>, has_data: False)
+      }
+    }
+    _ -> device
+  }
+}
+
+pub fn close(device: Device) {
+  case device.dev_type {
+    Default -> {
+      let assert option.Some(stream) = device.stream
+      let assert Ok(_) = file_stream.close(stream)
+      Nil
+    }
+    _ -> Nil
+  }
+}
diff --git a/sim/src/sim/machine.gleam b/sim/src/sim/machine.gleam
index 8ce6d54..b60fd00 100644
--- a/sim/src/sim/machine.gleam
+++ b/sim/src/sim/machine.gleam
@@ -1,17 +1,25 @@
 import gleam/bit_array
+import gleam/dict
+import gleam/int
 import gleam/list
+import gleam/order
 import gleam/result
 import gleam/string
+import sim/device
 import sim/loader
 import sim/memory
 import sim/registers
 
 pub type Machine {
-  Machine(memory: memory.Memory, registers: registers.Registers)
+  Machine(
+    memory: memory.Memory,
+    registers: registers.Registers,
+    devices: dict.Dict(Int, device.Device),
+  )
 }
 
 pub fn init(program: String) -> Machine {
-  Machine(loader.load_obj(program), registers.new())
+  Machine(loader.load_obj(program), registers.new(), dict.new())
 }
 
 pub fn state_string(machine: Machine) -> String {
@@ -66,6 +74,92 @@ fn fetch_instruction(
   }
 }
 
+fn get_operand34(machine: Machine, code: BitArray, size: Int) -> BitArray {
+  let assert <<_opcode:6, n:1, i:1, x:1, b:1, p:1, _e:1, offset:bits>> = code
+  let addr =
+    case b, p {
+      1, 0 -> memory.to_int(machine.registers.b) + memory.to_int(offset)
+      0, 1 -> memory.to_int(machine.registers.pc) + memory.to_int(offset)
+      0, 0 -> memory.to_int(offset)
+      _, _ -> panic
+    }
+    + case x {
+      0 -> 0
+      _ -> memory.to_int(machine.registers.x)
+    }
+  let getter = case size {
+    1 -> memory.get_char_at
+    3 -> memory.get_int_at
+    6 -> memory.get_float_at
+    _ -> panic
+  }
+  case n, i {
+    0, 1 -> memory.left_pad_to_length(<<addr>>, size * 8)
+    1, 1 -> getter(machine.memory, addr)
+    1, 0 ->
+      getter(
+        machine.memory,
+        memory.to_int(memory.get_int_at(machine.memory, addr)),
+      )
+    _, _ -> panic
+  }
+}
+
+fn get_address34(machine: Machine, code: BitArray, size: Int) -> BitArray {
+  let assert <<_opcode:6, n:1, i:1, x:1, b:1, p:1, _e:1, offset:bits>> = code
+  let addr =
+    case b, p {
+      1, 0 -> memory.to_int(machine.registers.b) + memory.to_int(offset)
+      0, 1 -> memory.to_int(machine.registers.pc) + memory.to_int(offset)
+      0, 0 -> memory.to_int(offset)
+      _, _ -> panic
+    }
+    + case x {
+      0 -> 0
+      _ -> memory.to_int(machine.registers.x)
+    }
+  let getter = case size {
+    1 -> memory.get_char_at
+    3 -> memory.get_int_at
+    6 -> memory.get_float_at
+    _ -> panic
+  }
+  case n, i {
+    0, 1 -> panic
+    1, 1 -> <<addr:24>>
+    1, 0 -> getter(machine.memory, addr)
+    _, _ -> panic
+  }
+}
+
+fn get_register(machine: Machine, code: Int) -> BitArray {
+  case code {
+    0 -> machine.registers.a
+    1 -> machine.registers.x
+    2 -> machine.registers.l
+    3 -> machine.registers.b
+    4 -> machine.registers.s
+    5 -> machine.registers.t
+    _ -> panic
+  }
+}
+
+fn set_register(
+  machine: Machine,
+  code: Int,
+  value: BitArray,
+) -> registers.Registers {
+  case code {
+    0 -> registers.Registers(..machine.registers, a: value)
+    1 -> registers.Registers(..machine.registers, x: value)
+    2 -> registers.Registers(..machine.registers, l: value)
+    3 -> registers.Registers(..machine.registers, b: value)
+    4 -> registers.Registers(..machine.registers, s: value)
+    5 -> registers.Registers(..machine.registers, t: value)
+    _ -> panic
+  }
+}
+
 pub fn step(machine: Machine, instructions: List(Def)) -> Machine {
   let assert <<pc:24>> = machine.registers.pc
 
@@ -124,252 +218,454 @@ pub fn get_def(instructions: List(Def), first_byte: BitArray) -> Def {
 pub fn get_instructions() -> List(Def) {
   [
     Def(6, 3, "ADD", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let operand = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.get_int_at(
-            machine.memory,
-            memory.to_int(machine.registers.pc) + memory.to_int(offset),
-          )
-        _ -> panic
-      }
+      let operand = get_operand34(machine, code, 3)
       Machine(
-        machine.memory,
-        registers.Registers(..machine.registers, a: <<
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: <<
           { memory.to_int(machine.registers.a) + memory.to_int(operand) }:24,
         >>),
       )
     }),
-    Def(22, 3, "ADDF", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(22, 3, "ADDF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(36, 2, "ADDR", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let assert <<_opcode:8, reg1:4, reg2:4>> = code
+      let assert <<operand1:24>> = get_register(machine, reg1)
+      let assert <<operand2:24>> = get_register(machine, reg2)
+      let value = operand2 + operand1
+      Machine(..machine, registers: set_register(machine, reg2, <<value:24>>))
     }),
-    Def(16, 3, "AND", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(16, 3, "AND", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(45, 2, "CLEAR", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let assert <<_opcode:8, reg1:4, _reg2:4>> = code
+      Machine(..machine, registers: set_register(machine, reg1, <<0:24>>))
     }),
     Def(10, 3, "COMP", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_operand34(machine, code, 3)
+      let sw = case bit_array.compare(machine.registers.a, operand) {
+        order.Lt -> <<0x80:24>>
+        order.Eq -> <<0:24>>
+        order.Gt -> <<0x40:24>>
+      }
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, sw: sw),
+      )
     }),
-    Def(34, 3, "COMPF", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(34, 3, "COMPF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(40, 2, "COMPR", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
-    }),
-    Def(9, 3, "DIV", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let operand = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.get_int_at(
-            machine.memory,
-            memory.to_int(machine.registers.pc) + memory.to_int(offset),
-          )
-        _ -> panic
+      let assert <<_opcode:8, reg1:4, reg2:4>> = code
+      let sw = case
+        bit_array.compare(
+          get_register(machine, reg1),
+          get_register(machine, reg2),
+        )
+      {
+        order.Lt -> <<0x80:24>>
+        order.Eq -> <<0:24>>
+        order.Gt -> <<0x40:24>>
       }
       Machine(
-        machine.memory,
-        registers.Registers(..machine.registers, a: <<
+        ..machine,
+        registers: registers.Registers(..machine.registers, sw: sw),
+      )
+    }),
+    Def(9, 3, "DIV", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: <<
           { memory.to_int(machine.registers.a) / memory.to_int(operand) }:24,
         >>),
       )
     }),
-    Def(25, 3, "DIVF", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(25, 3, "DIVF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(39, 2, "DIVR", fn(machine: Machine, code: BitArray) -> Machine {
+      let assert <<_opcode:8, reg1:4, reg2:4>> = code
+      let assert <<operand1:24>> = get_register(machine, reg1)
+      let assert <<operand2:24>> = get_register(machine, reg2)
+      let value = operand2 / operand1
+      Machine(..machine, registers: set_register(machine, reg2, <<value:24>>))
+    }),
+    Def(49, 1, "FIX", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(49, 1, "FIX", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(48, 1, "FLOAT", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(48, 1, "FLOAT", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
-    }),
-    Def(61, 1, "HIO", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(61, 1, "HIO", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(15, 3, "J", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let addr = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.to_int(machine.registers.pc) + memory.to_int(offset)
-        _ -> todo
-      }
+      let addr = get_address34(machine, code, 3)
       Machine(
-        machine.memory,
-        registers.Registers(..machine.registers, pc: <<addr:24>>),
+        ..machine,
+        registers: registers.Registers(..machine.registers, pc: addr),
       )
     }),
     Def(12, 3, "JEQ", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let addr = get_address34(machine, code, 3)
+      case machine.registers.sw {
+        <<0:24>> ->
+          Machine(
+            ..machine,
+            registers: registers.Registers(..machine.registers, pc: addr),
+          )
+        _ -> machine
+      }
     }),
     Def(13, 3, "JGT", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let addr = get_address34(machine, code, 3)
+      case machine.registers.sw {
+        <<0x40:24>> ->
+          Machine(
+            ..machine,
+            registers: registers.Registers(..machine.registers, pc: addr),
+          )
+        _ -> machine
+      }
     }),
     Def(14, 3, "JLT", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let addr = get_address34(machine, code, 3)
+      case machine.registers.sw {
+        <<0x80:24>> ->
+          Machine(
+            ..machine,
+            registers: registers.Registers(..machine.registers, pc: addr),
+          )
+        _ -> machine
+      }
     }),
     Def(18, 3, "JSUB", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let addr = get_address34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(
+          ..machine.registers,
+          l: machine.registers.pc,
+          pc: addr,
+        ),
+      )
     }),
     Def(0, 3, "LDA", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let operand = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.get_int_at(
-            machine.memory,
-            memory.to_int(machine.registers.pc) + memory.to_int(offset),
-          )
-        _ -> todo
-      }
+      let operand = get_operand34(machine, code, 3)
       Machine(
-        machine.memory,
-        registers.Registers(..machine.registers, a: operand),
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: operand),
       )
     }),
     Def(26, 3, "LDB", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, b: operand),
+      )
     }),
     Def(20, 3, "LDCH", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: <<
+          0:16,
+          operand:bits,
+        >>),
+      )
+    }),
+    Def(28, 3, "LDF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(28, 3, "LDF", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+    Def(2, 3, "LDL", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, l: operand),
+      )
     }),
-    Def(2, 3, "LDL", fn(machine: Machine, code: BitArray) -> Machine { machine }),
     Def(27, 3, "LDS", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, s: operand),
+      )
     }),
     Def(29, 3, "LDT", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, t: operand),
+      )
     }),
-    Def(1, 3, "LDX", fn(machine: Machine, code: BitArray) -> Machine { machine }),
-    Def(52, 3, "LPS", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(1, 3, "LDX", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_operand34(machine, code, 3)
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, x: operand),
+      )
+    }),
+    Def(52, 3, "LPS", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(8, 3, "MUL", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let operand = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.get_int_at(
-            machine.memory,
-            memory.to_int(machine.registers.pc) + memory.to_int(offset),
-          )
-        _ -> panic
-      }
+      let operand = get_operand34(machine, code, 3)
       Machine(
-        machine.memory,
-        registers.Registers(..machine.registers, a: <<
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: <<
           { memory.to_int(machine.registers.a) * memory.to_int(operand) }:24,
         >>),
       )
     }),
-    Def(24, 3, "MULF", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(24, 3, "MULF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(38, 2, "MULR", fn(machine: Machine, code: BitArray) -> Machine {
+      let assert <<_opcode:8, reg1:4, reg2:4>> = code
+      let assert <<operand1:24>> = get_register(machine, reg1)
+      let assert <<operand2:24>> = get_register(machine, reg2)
+      let value = operand2 * operand1
+      Machine(..machine, registers: set_register(machine, reg2, <<value:24>>))
+    }),
+    Def(50, 1, "NORM", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(50, 1, "NORM", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(17, 3, "OR", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(17, 3, "OR", fn(machine: Machine, code: BitArray) -> Machine { machine }),
-    Def(54, 3, "RD", fn(machine: Machine, code: BitArray) -> Machine { machine }),
-    Def(43, 2, "RMO", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(54, 3, "RD", fn(machine: Machine, code: BitArray) -> Machine {
+      let assert <<devnr:8>> = get_operand34(machine, code, 1)
+      let #(char, dev) = case dict.get(machine.devices, devnr) {
+        Ok(d) -> device.read(d)
+        Error(Nil) -> {
+          let d = device.open(int.to_base16(devnr) <> ".dev")
+          device.read(d)
+        }
+      }
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: <<
+          0:16,
+          char:bits,
+        >>),
+        devices: dict.insert(machine.devices, devnr, dev),
+      )
+    }),
+    Def(43, 2, "RMO", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(19, 3, "RSUB", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(19, 3, "RSUB", fn(machine: Machine, _code: BitArray) -> Machine {
+      Machine(
+        ..machine,
+        registers: registers.Registers(
+          ..machine.registers,
+          pc: machine.registers.l,
+        ),
+      )
+    }),
+    Def(41, 2, "SHIFTL", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(41, 2, "SHIFTL", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(42, 2, "SHIFTR", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(42, 2, "SHIFTR", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(60, 1, "SIO", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(60, 1, "SIO", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
-    }),
-    Def(59, 3, "SSK", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(59, 3, "SSK", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(3, 3, "STA", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let memory = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.set_int_at(
-            machine.memory,
-            memory.to_int(machine.registers.pc) + memory.to_int(offset),
-            machine.registers.a,
-          )
-        _ -> todo
-      }
-      Machine(memory, machine.registers)
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.a,
+        )
+
+      Machine(..machine, memory: memory)
     }),
     Def(30, 3, "STB", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.b,
+        )
+
+      Machine(..machine, memory: memory)
     }),
     Def(21, 3, "STCH", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_char_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.a,
+        )
+
+      Machine(..machine, memory: memory)
+    }),
+    Def(32, 3, "STF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(32, 3, "STF", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(53, 3, "STI", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(53, 3, "STI", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+    Def(5, 3, "STL", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.l,
+        )
+
+      Machine(..machine, memory: memory)
     }),
-    Def(5, 3, "STL", fn(machine: Machine, code: BitArray) -> Machine { machine }),
     Def(31, 3, "STS", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.s,
+        )
+
+      Machine(..machine, memory: memory)
     }),
     Def(58, 3, "STSW", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.sw,
+        )
+
+      Machine(..machine, memory: memory)
     }),
     Def(33, 3, "STT", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.t,
+        )
+
+      Machine(..machine, memory: memory)
+    }),
+    Def(4, 3, "STX", fn(machine: Machine, code: BitArray) -> Machine {
+      let operand = get_address34(machine, code, 3)
+      echo bit_array.base16_encode(operand)
+      let memory =
+        memory.set_int_at(
+          machine.memory,
+          memory.to_int(operand),
+          machine.registers.x,
+        )
+
+      Machine(..machine, memory: memory)
     }),
-    Def(4, 3, "STX", fn(machine: Machine, code: BitArray) -> Machine { machine }),
     Def(7, 3, "SUB", fn(machine: Machine, code: BitArray) -> Machine {
-      let assert <<_:12, offset:bits>> = code
-      let operand = case code {
-        <<_:6, 1:1, 1:1, 0:1, 0:1, 1:1, 0:1, _:bits>> ->
-          memory.get_int_at(
-            machine.memory,
-            memory.to_int(machine.registers.pc) + memory.to_int(offset),
-          )
-        _ -> panic
-      }
+      let operand = get_operand34(machine, code, 3)
       Machine(
-        machine.memory,
-        registers.Registers(..machine.registers, a: <<
+        ..machine,
+        registers: registers.Registers(..machine.registers, a: <<
           { memory.to_int(machine.registers.a) - memory.to_int(operand) }:24,
         >>),
       )
     }),
-    Def(23, 3, "SUBF", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(23, 3, "SUBF", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(23, 2, "SUBR", fn(machine: Machine, code: BitArray) -> Machine {
+      let assert <<_opcode:8, reg1:4, reg2:4>> = code
+      let assert <<operand1:24>> = get_register(machine, reg1)
+      let assert <<operand2:24>> = get_register(machine, reg2)
+      let value = operand2 - operand1
+      Machine(..machine, registers: set_register(machine, reg2, <<value:24>>))
+    }),
+    Def(23, 2, "SVC", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
-    Def(23, 2, "SVC", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+    Def(23, 3, "TD", fn(machine: Machine, code: BitArray) -> Machine {
+      let assert <<devnr:8>> = get_operand34(machine, code, 1)
+      let #(dev, machine) = case dict.get(machine.devices, devnr) {
+        Ok(d) -> #(d, machine)
+        Error(Nil) -> {
+          let d = device.open(int.to_base16(devnr) <> ".dev")
+          #(
+            d,
+            Machine(..machine, devices: dict.insert(machine.devices, devnr, d)),
+          )
+        }
+      }
+      let dev = device.test_device(dev)
+      Machine(
+        ..machine,
+        devices: dict.insert(machine.devices, devnr, dev),
+        registers: registers.Registers(..machine.registers, sw: <<0x40:24>>),
+      )
     }),
-    Def(23, 3, "TD", fn(machine: Machine, code: BitArray) -> Machine { machine }),
-    Def(23, 1, "TIO", fn(machine: Machine, code: BitArray) -> Machine {
+    Def(23, 1, "TIO", fn(machine: Machine, _code: BitArray) -> Machine {
       machine
     }),
     Def(23, 3, "TIX", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let assert <<x:24>> = machine.registers.x
+      let x = x + 1
+      let operand = get_operand34(machine, code, 3)
+      let sw = case bit_array.compare(machine.registers.x, operand) {
+        order.Lt -> <<0x80:24>>
+        order.Eq -> <<0:24>>
+        order.Gt -> <<0x40:24>>
+      }
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, sw: sw, x: <<x:24>>),
+      )
     }),
     Def(23, 2, "TIXR", fn(machine: Machine, code: BitArray) -> Machine {
-      machine
+      let assert <<x:24>> = machine.registers.x
+      let x = x + 1
+      let assert <<_opcode:8, reg1:4, _reg2:4>> = code
+      let sw = case
+        bit_array.compare(machine.registers.x, get_register(machine, reg1))
+      {
+        order.Lt -> <<0x80:24>>
+        order.Eq -> <<0:24>>
+        order.Gt -> <<0x40:24>>
+      }
+      Machine(
+        ..machine,
+        registers: registers.Registers(..machine.registers, sw: sw, x: <<x:24>>),
+      )
+    }),
+    Def(23, 3, "WD", fn(machine: Machine, code: BitArray) -> Machine {
+      let assert <<devnr:8>> = get_operand34(machine, code, 1)
+      let assert <<_:16, char:bits>> = machine.registers.a
+      let dev = case dict.get(machine.devices, devnr) {
+        Ok(d) -> device.write(d, char)
+        Error(Nil) -> {
+          let d = device.open(int.to_base16(devnr) <> ".dev")
+          device.write(d, char)
+        }
+      }
+      Machine(..machine, devices: dict.insert(machine.devices, devnr, dev))
     }),
-    Def(23, 3, "WD", fn(machine: Machine, code: BitArray) -> Machine { machine }),
   ]
 }
diff --git a/sim/src/sim/memory.gleam b/sim/src/sim/memory.gleam
index d3a2835..88ff75a 100644
--- a/sim/src/sim/memory.gleam
+++ b/sim/src/sim/memory.gleam
@@ -3,7 +3,7 @@ import gleam/bit_array
 pub type Memory =
   BitArray
 
-fn pad_to_length(memory: Memory, lenght: Int) -> Memory {
+pub fn pad_to_length(memory: Memory, lenght: Int) -> Memory {
   case bit_array.bit_size(memory) < lenght {
     True -> {
       pad_to_length(<<memory:bits, 0:1>>, lenght)
@@ -12,20 +12,29 @@ fn pad_to_length(memory: Memory, lenght: Int) -> Memory {
   }
 }
 
-pub fn insert_at(memory: Memory, pos: Int, value: BitArray) -> Memory {
-  let memory = case pos >= bit_array.bit_size(memory) {
+pub fn left_pad_to_length(memory: Memory, lenght: Int) -> Memory {
+  case bit_array.bit_size(memory) < lenght {
     True -> {
-      pad_to_length(memory, pos)
+      pad_to_length(<<0:1, memory:bits>>, lenght)
+    }
+    _ -> memory
+  }
+}
+
+pub fn insert_at(memory: Memory, pos: Int, value: BitArray) -> Memory {
+  let memory = case pos > bit_array.byte_size(memory) {
+    True -> {
+      pad_to_length(memory, pos * 8)
     }
     False -> memory
   }
-  let length = bit_array.bit_size(value)
+  let length = bit_array.byte_size(value)
   let assert Ok(head) = bit_array.slice(memory, 0, pos)
   case
     bit_array.slice(
       memory,
       pos + length,
-      bit_array.bit_size(memory) - pos - length,
+      bit_array.byte_size(memory) - pos - length,
     )
   {
     Ok(tail) -> <<head:bits, value:bits, tail:bits>>
@@ -52,7 +61,7 @@ pub fn set_int_at(memory: Memory, pos: Int, value: BitArray) -> Memory {
 }
 
 pub fn get_float_at(memory: Memory, pos: Int) -> BitArray {
-  let assert Ok(value) = bit_array.slice(memory, pos, 5)
+  let assert Ok(value) = bit_array.slice(memory, pos, 6)
   value
 }
 
diff --git a/sim/test/sim_test.gleam b/sim/test/sim_test.gleam
index fba3c88..0cc33bd 100644
--- a/sim/test/sim_test.gleam
+++ b/sim/test/sim_test.gleam
@@ -1,4 +1,6 @@
 import gleeunit
+import sim/device
+import sim/memory
 
 pub fn main() -> Nil {
   gleeunit.main()
@@ -11,3 +13,35 @@ pub fn hello_world_test() {
 
   assert greeting == "Hello, Joe!"
 }
+
+pub fn pad_test() {
+  assert <<1, 2, 3, 0>> == memory.pad_to_length(<<1, 2, 3>>, 32)
+}
+
+pub fn insert_test() {
+  assert <<1, 2, 3, 4>> == memory.insert_at(<<1, 2, 3>>, 3, <<4>>)
+  assert <<1, 2, 3, 0, 5>> == memory.insert_at(<<1, 2, 3>>, 4, <<5>>)
+  assert <<1, 67, 3>> == memory.insert_at(<<1, 2, 3>>, 1, <<67>>)
+}
+
+pub fn open_test() {
+  let d0 = device.open("0")
+  device.close(d0)
+}
+
+pub fn test_device_test() {
+  let d1 = device.open("1")
+  assert <<>> == device.read(d1).0
+  let d1 = device.test_device(d1)
+  assert d1.has_data == True
+  let #(char, d1) = device.read(d1)
+  assert <<"a">> == char
+  assert d1.has_data == False
+  assert <<>> == device.read(d1).0
+  device.close(d1)
+
+  let d0 = device.open("0")
+  let d0 = device.test_device(d0)
+  assert d0.has_data == False
+  device.close(d0)
+}