diff --git a/src/bus/four_wire.rs b/src/bus/four_wire.rs
index 684262a..d94524f 100644
--- a/src/bus/four_wire.rs
+++ b/src/bus/four_wire.rs
@@ -1,15 +1,13 @@
 use embedded_hal::digital::v2::OutputPin;
 use embedded_hal::spi::FullDuplex;
 
-use crate::bus::Bus;
+use crate::bus::{ActiveBus, Bus};
 
 pub struct FourWire<ChipSelect: OutputPin> {
-    cs: ChipSelect
+    cs: ChipSelect,
 }
 
-impl<ChipSelect: OutputPin>
-    FourWire<ChipSelect>
-{
+impl<ChipSelect: OutputPin> FourWire<ChipSelect> {
     pub fn new(cs: ChipSelect) -> Self {
         Self { cs }
     }
@@ -18,12 +16,22 @@ impl<ChipSelect: OutputPin>
     }
 }
 
-impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> Bus<Spi>
-    for FourWire<ChipSelect>
-{
+impl<ChipSelect: OutputPin> Bus for FourWire<ChipSelect> {}
+
+impl<ChipSelect: OutputPin> FourWire<ChipSelect> {
+    pub fn activate<Spi: FullDuplex<u8>>(self, spi: Spi) -> ActiveFourWire<Spi, ChipSelect> {
+        ActiveFourWire { cs: self.cs, spi }
+    }
+}
+
+pub struct ActiveFourWire<Spi: FullDuplex<u8>, ChipSelect: OutputPin> {
+    cs: ChipSelect,
+    spi: Spi,
+}
+
+impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> ActiveBus for ActiveFourWire<Spi, ChipSelect> {
     type Error = FourWireError<Spi::Error, ChipSelect::Error>;
-    fn transfer_frame<'a, 'b>(
-        spi: &'b mut Spi,
+    fn transfer_frame<'a>(
         address_phase: [u8; 2],
         control_phase: u8,
         data_phase: &'a mut [u8],
@@ -32,6 +40,11 @@ impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> Bus<Spi>
         Ok(data_phase)
     }
 }
+impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> ActiveFourWire<Spi, ChipSelect> {
+    pub fn deactivate(self) -> (FourWire<ChipSelect>, Spi) {
+        (FourWire::new(self.cs), self.spi)
+    }
+}
 
 pub enum FourWireError<SpiError, ChipSelectError> {
     SpiError(SpiError),
diff --git a/src/bus/mod.rs b/src/bus/mod.rs
index f962138..3032b52 100644
--- a/src/bus/mod.rs
+++ b/src/bus/mod.rs
@@ -1,16 +1,18 @@
 use nb::Result;
-use embedded_hal::spi::FullDuplex;
 
 mod four_wire;
 mod three_wire;
 
+pub use self::four_wire::ActiveFourWire;
 pub use self::four_wire::FourWire;
+pub use self::three_wire::ActiveThreeWire;
 pub use self::three_wire::ThreeWire;
 
-pub trait Bus<Spi: FullDuplex<u8>> {
+pub trait Bus {}
+
+pub trait ActiveBus {
     type Error;
-    fn transfer_frame<'a, 'b>(
-        spi: &'b mut Spi,
+    fn transfer_frame<'a>(
         address_phase: [u8; 2],
         control_phase: u8,
         data_phase: &'a mut [u8],
diff --git a/src/bus/three_wire.rs b/src/bus/three_wire.rs
index 787ae0d..07db70f 100644
--- a/src/bus/three_wire.rs
+++ b/src/bus/three_wire.rs
@@ -1,19 +1,30 @@
 use embedded_hal::spi::FullDuplex;
 
-use crate::bus::Bus;
+use crate::bus::{ActiveBus, Bus};
 
 pub struct ThreeWire {}
 
 impl ThreeWire {
     pub fn new() -> Self {
-        Self { }
+        Self {}
     }
 }
 
-impl<Spi: FullDuplex<u8>> Bus<Spi> for ThreeWire {
+impl Bus for ThreeWire {}
+
+impl ThreeWire {
+    pub fn activate<Spi: FullDuplex<u8>>(self, spi: Spi) -> ActiveThreeWire<Spi> {
+        ActiveThreeWire { spi }
+    }
+}
+
+pub struct ActiveThreeWire<Spi: FullDuplex<u8>> {
+    spi: Spi,
+}
+
+impl<Spi: FullDuplex<u8>> ActiveBus for ActiveThreeWire<Spi> {
     type Error = Spi::Error;
-    fn transfer_frame<'a, 'b>(
-        spi: &'b mut Spi,
+    fn transfer_frame<'a>(
         address_phase: [u8; 2],
         control_phase: u8,
         data_phase: &'a mut [u8],
@@ -22,3 +33,9 @@ impl<Spi: FullDuplex<u8>> Bus<Spi> for ThreeWire {
         Ok(data_phase)
     }
 }
+
+impl<Spi: FullDuplex<u8>> ActiveThreeWire<Spi> {
+    pub fn deactivate(self) -> (ThreeWire, Spi) {
+        (ThreeWire::new(), self.spi)
+    }
+}
diff --git a/src/inactive_w5500.rs b/src/inactive_w5500.rs
new file mode 100644
index 0000000..3bc7f7f
--- /dev/null
+++ b/src/inactive_w5500.rs
@@ -0,0 +1,26 @@
+use bus::{ActiveFourWire, ActiveThreeWire, Bus, FourWire, ThreeWire};
+use embedded_hal::digital::v2::OutputPin;
+use embedded_hal::spi::FullDuplex;
+use w5500::W5500;
+
+pub struct InactiveW5500<SpiBus: Bus> {
+    bus: SpiBus,
+}
+
+impl<SpiBus: Bus> InactiveW5500<SpiBus> {
+    pub fn new(bus: SpiBus) -> Self {
+        Self { bus }
+    }
+}
+
+impl<ChipSelect: OutputPin> InactiveW5500<FourWire<ChipSelect>> {
+    pub fn activate<Spi: FullDuplex<u8>>(self, spi: Spi) -> W5500<ActiveFourWire<Spi, ChipSelect>> {
+        W5500::new(self.bus.activate(spi))
+    }
+}
+
+impl InactiveW5500<ThreeWire> {
+    pub fn activate<Spi: FullDuplex<u8>>(self, spi: Spi) -> W5500<ActiveThreeWire<Spi>> {
+        W5500::new(self.bus.activate(spi))
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index b1f5d90..44ce24e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -901,7 +901,7 @@ extern crate nb;
 //     }
 // }
 
-
-pub mod uninitialized_w5500;
 pub mod bus;
+pub mod inactive_w5500;
+pub mod uninitialized_w5500;
 pub mod w5500;
diff --git a/src/uninitialized_w5500.rs b/src/uninitialized_w5500.rs
index d4badc8..638c84e 100644
--- a/src/uninitialized_w5500.rs
+++ b/src/uninitialized_w5500.rs
@@ -1,34 +1,33 @@
-use embedded_hal::spi::FullDuplex;
+use bus::{ActiveBus, ActiveFourWire, ActiveThreeWire};
 use embedded_hal::digital::v2::OutputPin;
-use bus::{Bus, FourWire, ThreeWire};
+use embedded_hal::spi::FullDuplex;
 use w5500::W5500;
 
-pub struct UninitializedW5500<Spi: FullDuplex<u8>, SpiBus: Bus<Spi>> {
+pub struct UninitializedW5500<SpiBus: ActiveBus> {
     bus: SpiBus,
-    spi: Spi,
 }
 
-impl<Spi: FullDuplex<u8>, SpiBus: Bus<Spi>> UninitializedW5500<Spi, SpiBus> {
-    pub fn initialize() -> W5500 {
+impl<SpiBus: ActiveBus> UninitializedW5500<SpiBus> {
+    pub fn initialize(self) -> W5500<SpiBus> {
         // TODO actually initialize chip
-        W5500 {}
+        W5500::new(self.bus)
+    }
+    pub fn new(bus: SpiBus) -> UninitializedW5500<SpiBus> {
+        UninitializedW5500 { bus: bus }
     }
 }
 
-impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> UninitializedW5500<Spi, FourWire<ChipSelect>> {
-    pub fn new(spi: Spi, cs: ChipSelect) -> Self {
-        Self { spi, bus: FourWire::new(cs) }
-    }
+impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin>
+    UninitializedW5500<ActiveFourWire<Spi, ChipSelect>>
+{
     pub fn deactivate(self) -> (Spi, ChipSelect) {
-        (self.spi, self.bus.release())
+        let (bus, spi) = self.bus.deactivate();
+        (spi, bus.release())
     }
 }
 
-impl<Spi: FullDuplex<u8>> UninitializedW5500<Spi, ThreeWire> {
-    pub fn new(spi: Spi) -> Self {
-        Self { spi, bus: ThreeWire::new() }
-    }
+impl<Spi: FullDuplex<u8>> UninitializedW5500<ActiveThreeWire<Spi>> {
     pub fn deactivate(self) -> Spi {
-        self.spi
+        self.bus.deactivate().1
     }
-}
\ No newline at end of file
+}
diff --git a/src/w5500.rs b/src/w5500.rs
index 1650ef6..02acdad 100644
--- a/src/w5500.rs
+++ b/src/w5500.rs
@@ -1 +1,34 @@
-pub struct W5500 {}
\ No newline at end of file
+use crate::inactive_w5500::InactiveW5500;
+use crate::uninitialized_w5500::UninitializedW5500;
+use bus::{ActiveBus, ActiveFourWire, ActiveThreeWire, FourWire, ThreeWire};
+use embedded_hal::digital::v2::OutputPin;
+use embedded_hal::spi::FullDuplex;
+
+pub struct W5500<SpiBus: ActiveBus> {
+    bus: SpiBus,
+}
+
+impl<SpiBus: ActiveBus> W5500<SpiBus> {
+    pub fn new(bus: SpiBus) -> Self {
+        W5500 { bus }
+    }
+    pub fn reset(self) -> UninitializedW5500<SpiBus> {
+        // TODO reset chip
+        UninitializedW5500::new(self.bus)
+    }
+    //TODO open_udp_socket
+}
+
+impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> W5500<ActiveFourWire<Spi, ChipSelect>> {
+    pub fn deactivate(self) -> (InactiveW5500<FourWire<ChipSelect>>, Spi) {
+        let (bus, spi) = self.bus.deactivate();
+        (InactiveW5500::new(bus), spi)
+    }
+}
+
+impl<Spi: FullDuplex<u8>> W5500<ActiveThreeWire<Spi>> {
+    pub fn deactivate(self) -> (InactiveW5500<ThreeWire>, Spi) {
+        let (bus, spi) = self.bus.deactivate();
+        (InactiveW5500::new(bus), spi)
+    }
+}