diff --git a/stackline/src/context.rs b/stackline/src/context.rs
index ff39fea..ff3156d 100644
--- a/stackline/src/context.rs
+++ b/stackline/src/context.rs
@@ -18,6 +18,7 @@ use super::*;
 pub struct UpdateContext<'a> {
     position: (usize, usize),
     pane: *const Pane,
+    state: &'a mut State,
 
     phantom: PhantomData<&'a Pane>,
 }
@@ -27,15 +28,16 @@ impl<'a> UpdateContext<'a> {
     pub(crate) fn new(pane: &'a mut Pane, position: (usize, usize)) -> Option<(Self, &'a mut AnyTile)> {
 
         let ptr: *const Pane = &*pane;
-        let tile = pane.get_mut(position)?.get_mut()?;
+        let (tile, _signal, state) = pane.get_mut(position)?.into_raw_mut();
 
         let res = Self {
             position,
             pane: ptr,
+            state,
             phantom: PhantomData
         };
 
-        Some((res, tile))
+        Some((res, tile.as_mut()?))
     }
 
     #[inline]
@@ -51,6 +53,21 @@ impl<'a> UpdateContext<'a> {
         pane.get(self.position).unwrap().signal()
     }
 
+    #[inline]
+    pub fn state(&self) -> State {
+        *self.state
+    }
+
+    #[inline]
+    pub fn set_state(&mut self, state: State) {
+        *self.state = state;
+    }
+
+    #[inline]
+    pub fn next_state(&mut self) {
+        *self.state = self.state.next();
+    }
+
     /// Returns an immutable reference to the [FullTile] at `pos` in the current [Pane].
     /// Returns `None` if the tile is the current tile (see [UpdateContext]) or if it does not exist.
     #[inline]
@@ -74,6 +91,12 @@ impl<'a> UpdateContext<'a> {
         pane.offset(self.position, offset)
     }
 
+    /// Shortcut for calling both `ctx.offset(offset)` and `ctx.get(pos)`
+    #[inline]
+    pub fn get_offset<'b>(&'b self, offset: (i8, i8)) -> Option<((usize, usize), &'b FullTile)> where 'a: 'b {
+        self.offset(offset).and_then(|pos| self.get(pos).map(|tile| (pos, tile)))
+    }
+
     // SAFETY: `self.pane` originates from a `&'a mut Pane`,
     // guaranteeing that no accesses may be done outside of ours.
     // No access to `pane[position].cell` may be done!
@@ -88,8 +111,9 @@ impl<'a> UpdateContext<'a> {
 ///
 /// During this phase, the tile may access itself through an immutable borrow and its signal through an owned reference.
 /// It may access the other tiles immutably, but it cannot access the other signals.
+/// It can read and modify any tile's state.
 
-// SAFETY: this structures ensures that it has exlusive, mutable access to `∀x, pane[x].signal` and `pane.signals`.
+// SAFETY: this structures ensures that it has exlusive, mutable access to `∀x, pane[x].signal, pane[x].state` and `pane.signals`.
 // Other parts of `pane` may be accessed and returned immutably.
 pub struct TransmitContext<'a> {
     position: (usize, usize),
@@ -132,14 +156,58 @@ impl<'a> TransmitContext<'a> {
         pane.get(pos)?.get()
     }
 
+    /// Returns the state of the tile at `pos` in the current [Pane]
+    #[inline]
+    pub fn get_state(&self, pos: (usize, usize)) -> Option<State> {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: we only return a copy of pane[pos].state
+        Some(pane.get(pos)?.state())
+    }
+
+    /// Sets the state of the tile at `pos` in the current [Pane]
+    #[inline]
+    pub fn set_state(&self, pos: (usize, usize), state: State) -> Option<()> {
+        let pane = unsafe { self.pane_mut() };
+
+        // SAFETY: there are no borrows of pane[pos].state
+        pane.get_mut(pos)?.set_state(state);
+        Some(())
+    }
+
+    /// Returns whether or not the tile at `pos` accepts a signal coming from `direction`.
+    /// If the tile does not exist, then this function will return `false`.
+    #[inline]
+    pub fn accepts_signal(&self, pos: (usize, usize), direction: Direction) -> bool {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: does not access `pane[pos].signal`
+        match pane.get(pos) {
+            Some(tile) => tile.accepts_signal(direction),
+            None => false
+        }
+    }
+
     /// Sends a signal to be stored in a cell (may be the current one), the signal overrides that of the other cell
-    /// Returns true if the signal was stored in a cell, false otherwise
-    pub fn send<'b>(&'b self, pos: (usize, usize), signal: Signal) -> Option<Weak<Signal>> where 'a: 'b {
+    /// Returns true if the signal was stored in a cell, false otherwise.
+    /// The target cell's state will be set to `Active` if it received the signal.
+    /// The signal's `position` will be set to `pos`.
+    pub fn send<'b>(&'b mut self, pos: (usize, usize), mut signal: Signal) -> Option<Weak<Signal>> where 'a: 'b {
         // SAFETY: we do not return any reference to any data borrowed in this function
-        // SAFETY: we only access `pane[pos].signal` and `pane.signals`
+        // SAFETY: we only access `pane[pos].signal`, `pane[pos].state` and `pane.signals`
         let pane = unsafe { self.pane_mut() };
 
-        pane.set_signal(pos, signal)
+        signal.set_position(pos);
+
+        match pane.set_signal(pos, signal) {
+            Some(signal) => {
+                // SAFETY: we only access `pane[pos].state`
+                pane.get_mut(pos).unwrap_or_else(|| unreachable!()).set_state(State::Active);
+
+                Some(signal)
+            }
+            None => None
+        }
     }
 
     /// Returns `Some((position.x + Δx, position.y + Δy))` iff `(x + Δx, y + Δy)` is inside the pane
diff --git a/stackline/src/pane.rs b/stackline/src/pane.rs
index 6aa4f6d..5b5ff07 100644
--- a/stackline/src/pane.rs
+++ b/stackline/src/pane.rs
@@ -65,6 +65,10 @@ impl Pane {
         self.tiles.get_mut(position.1 * self.width.get() + position.0)
     }
 
+    /// Sets the signal for the tile at `position` to `signal`.
+    /// Returns `Some` iff:
+    /// - the tile exists
+    /// - the tile accepts a signal (ie. it isn't empty)
     // SAFETY: may only access `self[pos].signal` and `self.signals`
     #[inline]
     pub fn set_signal(&mut self, position: (usize, usize), signal: Signal) -> Option<Weak<Signal>> {
@@ -87,7 +91,17 @@ impl Pane {
         Some(())
     }
 
-    // TODO: update_all (requires FullTile::state)
+    pub fn update_all(&mut self) {
+        for y in 0..self.height.get() {
+            for x in 0..self.width.get() {
+                if let Some((ctx, tile)) = UpdateContext::new(self, (x, y)) {
+                    if ctx.state() != State::Idle {
+                        tile.update(ctx);
+                    }
+                }
+            }
+        }
+    }
 
     #[inline]
     pub fn transmit(&mut self, position: (usize, usize)) -> Option<()> {
diff --git a/stackline/src/signal.rs b/stackline/src/signal.rs
index d9a1524..e4a2a58 100644
--- a/stackline/src/signal.rs
+++ b/stackline/src/signal.rs
@@ -33,4 +33,8 @@ impl Signal {
     pub fn position(&self) -> (usize, usize) {
         self.position
     }
+
+    pub(crate) fn set_position(&mut self, position: (usize, usize)) {
+        self.position = position;
+    }
 }
diff --git a/stackline/src/tile/mod.rs b/stackline/src/tile/mod.rs
index 3f2718f..86f5da4 100644
--- a/stackline/src/tile/mod.rs
+++ b/stackline/src/tile/mod.rs
@@ -18,18 +18,23 @@ Cloning a `FullTile` results in a `FullTile` that does not have any signal.
 pub struct FullTile {
     cell: Option<AnyTile>,
     signal: Option<Rc<Signal>>,
-    // TODO: state
+    state: State,
 }
 
 // SAFETY: should not implement Tile
 impl FullTile {
     pub fn new(cell: Option<AnyTile>) -> Self {
-        Self { cell, signal: None }
+        Self {
+            cell,
+            signal: None,
+            state: State::default()
+        }
     }
 
+    // SAFETY: must not access `self.signal`
     pub fn accepts_signal(&self, direction: Direction) -> bool {
         match self.cell {
-            Some(ref tile) => tile.accepts_signal(direction),
+            Some(ref tile) => self.state.accepts_signal() && tile.accepts_signal(direction),
             None => false,
         }
     }
@@ -52,6 +57,12 @@ impl FullTile {
         self.cell.as_ref()
     }
 
+    /// Returns a mutable reference to the internal state of this tile
+    #[inline]
+    pub fn get_mut<'b>(&'b mut self) -> Option<&'b mut AnyTile> {
+        self.cell.as_mut()
+    }
+
     /// Returns the signal of this tile
     #[inline]
     pub fn signal<'b>(&'b self) -> Option<&'b Rc<Signal>> {
@@ -59,13 +70,29 @@ impl FullTile {
     }
 
     #[inline]
-    pub(crate) fn take_signal(&mut self) -> Option<Rc<Signal>> {
+    pub fn take_signal(&mut self) -> Option<Rc<Signal>> {
         std::mem::take(&mut self.signal)
     }
 
+    // SAFETY: may only access `self.state`
     #[inline]
-    pub(crate) fn get_mut<'b>(&'b mut self) -> Option<&'b mut AnyTile> {
-        self.cell.as_mut()
+    pub fn state(&self) -> State {
+        self.state
+    }
+
+    // SAFETY: may only access `self.state`
+    #[inline]
+    pub fn set_state(&mut self, state: State) {
+        self.state = state
+    }
+
+    #[inline]
+    pub fn next_state(&mut self) {
+        self.state = self.state.next();
+    }
+
+    pub fn into_raw_mut<'b>(&'b mut self) -> (&'b mut Option<AnyTile>, &'b mut Option<Rc<Signal>>, &'b mut State) {
+        (&mut self.cell, &mut self.signal, &mut self.state)
     }
 }
 
@@ -94,7 +121,9 @@ pub trait Tile: DynClone + std::fmt::Debug {
     /// Function to be called when the tile needs to update its internal state.
     /// During the "update" phase, the tile may access its signal and the other tiles immutably.
     #[inline]
-    fn update<'b>(&'b mut self, _context: UpdateContext<'b>) {}
+    fn update<'b>(&'b mut self, mut context: UpdateContext<'b>) {
+        context.next_state();
+    }
 
     /// Function that will be called if the tile has a signal.
     fn transmit<'b>(&'b self, signal: Rc<Signal>, context: TransmitContext<'b>);
diff --git a/stackline/src/tile/wire.rs b/stackline/src/tile/wire.rs
index 1b95498..7e36a5d 100644
--- a/stackline/src/tile/wire.rs
+++ b/stackline/src/tile/wire.rs
@@ -12,16 +12,15 @@ impl Wire {
 }
 
 impl Tile for Wire {
-    fn transmit<'b>(&'b self, signal: Rc<Signal>, context: TransmitContext<'b>) {
+    fn transmit<'b>(&'b self, signal: Rc<Signal>, mut context: TransmitContext<'b>) {
         for &direction in self.0.into_directions() {
             if direction == signal.direction().opposite() {
                 continue;
             }
 
-            if let Some(new_pos) = context.offset(direction.into_offset()) {
-                let tile = context.get(new_pos);
-                if tile.map(|t| t.accepts_signal(direction)).unwrap_or(false) {
-                    context.send(new_pos, signal.clone_move(direction).unwrap());
+            if let Some(pos) = context.offset(direction.into_offset()) {
+                if context.accepts_signal(pos, direction) {
+                    context.send(pos, signal.clone_move(direction).unwrap_or_else(|| unreachable!()));
                 }
             }
         }
@@ -41,18 +40,15 @@ impl Diode {
     }
 }
 
-// impl Tile for Diode {
-//     fn update(&mut self, world: &mut World, signal: &mut Option<Rc<Signal>>, pos: (usize, usize)) {
-//         if let Some(signal) = std::mem::take(signal) {
-//             if let Some(new_pos) = world.offset(pos, self.0.into_offset()) {
-//                 let tile = world.get(new_pos).unwrap();
-//                 if tile.borrow().accepts_signal(self.0) {
-//                     world.send_signal(new_pos, (*signal).clone_with_dir(self.0)).unwrap();
-//                 }
-//             }
-//         }
-//     }
-// }
+impl Tile for Diode {
+    fn transmit<'b>(&'b self, signal: Rc<Signal>, mut context: TransmitContext<'b>) {
+        if let Some(pos) = context.offset(self.0.into_offset()) {
+            if context.accepts_signal(pos, self.0) {
+                context.send(pos, signal.clone_move(self.0).unwrap_or_else(|| unreachable!()));
+            }
+        }
+    }
+}
 
 #[cfg(test)]
 mod test {
@@ -70,6 +66,7 @@ mod test {
         // Test the signal going from left to right
         test_set_signal!(pane, (0, 0), Direction::Right);
 
+        pane.update_all();
         pane.transmit_all();
 
         assert_signal!(pane, (1, 0));
@@ -77,6 +74,7 @@ mod test {
         assert_no_signal!(pane, (2, 0));
         assert_no_signal!(pane, (1, 1));
 
+        pane.update_all();
         pane.transmit_all();
 
         assert_signal!(pane, (2, 0));
@@ -84,14 +82,20 @@ mod test {
         assert_no_signal!(pane, (0, 0));
         assert_no_signal!(pane, (1, 0));
 
+        pane.update_all();
         pane.transmit_all();
         for (_, _, tile) in pane.tiles() {
             assert!(tile.signal().is_none());
         }
 
+        // Let the simulation cool down
+        pane.update_all();
+        pane.update_all();
+
         // Test the signal going from right to left
         test_set_signal!(pane, (2, 0), Direction::Left);
 
+        pane.update_all();
         pane.transmit_all();
 
         assert_signal!(pane, (1, 0));
@@ -99,6 +103,7 @@ mod test {
         assert_no_signal!(pane, (2, 0));
         assert_no_signal!(pane, (1, 1));
 
+        pane.update_all();
         pane.transmit_all();
 
         assert_signal!(pane, (0, 0));
diff --git a/stackline/src/utils.rs b/stackline/src/utils.rs
index c71d482..9b36060 100644
--- a/stackline/src/utils.rs
+++ b/stackline/src/utils.rs
@@ -17,6 +17,16 @@ pub enum Direction {
     Right,
 }
 
+/// Represents the state that a cell may be in. The usual state transition schema is `Idle → Active → Dormant → Idle`.
+/// A tile will only be [`update`d](Tile::update) if it is in the `Active` or `Dormant` state.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+pub enum State {
+    Idle,
+    Active,
+    Dormant,
+}
+
 const HORIZONTAL: [Direction; 2] = [Direction::Left, Direction::Right];
 const VERTICAL: [Direction; 2] = [Direction::Up, Direction::Down];
 const ANY: [Direction; 4] = [
@@ -75,6 +85,34 @@ impl Direction {
     }
 }
 
+impl State {
+    /// Rotates the state:
+    /// - `Idle → Active`
+    /// - `Active → Dormant`
+    /// - `Dormant → Idle`
+    pub fn next(self) -> Self {
+        match self {
+            State::Idle => State::Active,
+            State::Active => State::Dormant,
+            State::Dormant => State::Idle,
+        }
+    }
+
+    /// Returns true if `Idle`
+    pub fn accepts_signal(self) -> bool {
+        match self {
+            State::Idle => true,
+            _ => false,
+        }
+    }
+}
+
+impl Default for State {
+    fn default() -> Self {
+        State::Idle
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -92,4 +130,23 @@ mod test {
             }
         }
     }
+
+    #[test]
+    fn test_state_next_rotate_3() {
+        let state = State::default();
+
+        assert_eq!(state, State::Idle);
+        assert!(state.accepts_signal());
+
+        let state = state.next();
+        assert_eq!(state, State::Active);
+        assert!(!state.accepts_signal());
+
+        let state = state.next();
+        assert_eq!(state, State::Dormant);
+        assert!(!state.accepts_signal());
+
+        let state = state.next();
+        assert_eq!(state, State::Idle);
+    }
 }