diff --git a/CHANGELOG.md b/CHANGELOG.md
index 504c383a1..16f63e504 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   importing the `nb` crate directly in dependendent crates.
 - `blocking::Serial`: renamed `bwrite_all` to `write`, `bflush` to `flush.
 - Removed `prelude` to avoid method name conflicts between different flavors (blocking, nb) of the same trait. Traits must now be manually imported.
+- The serial, spi, and adc traits where changed to use associated `Word` types instead of type parameters
 
 ### Removed
 - Removed random number generation (`rng`) traits in favor of [rand_core](https://crates.io/crates/rand_core).
diff --git a/src/blocking/serial.rs b/src/blocking/serial.rs
index 5967414a1..515446a15 100644
--- a/src/blocking/serial.rs
+++ b/src/blocking/serial.rs
@@ -1,7 +1,10 @@
 //! Blocking serial API
 
 /// Write half of a serial interface (blocking variant)
-pub trait Write<Word> {
+pub trait Write {
+    /// Word type
+    type Word;
+
     /// The type of error that can occur when writing
     type Error;
 
@@ -13,7 +16,7 @@ pub trait Write<Word> {
     /// everything has been sent, call [`flush`] after this function returns.
     ///
     /// [`flush`]: #tymethod.flush
-    fn write(&mut self, buffer: &[Word]) -> Result<(), Self::Error>;
+    fn write(&mut self, buffer: &[Self::Word]) -> Result<(), Self::Error>;
 
     /// Block until the serial interface has sent all buffered words
     fn flush(&mut self) -> Result<(), Self::Error>;
@@ -29,16 +32,17 @@ pub mod write {
     ///
     /// [`nonblocking::serial::Write`]: ../../nonblocking/serial/trait.Write.html
     /// [`blocking::serial::Write`]: ../trait.Write.html
-    pub trait Default<Word>: crate::nb::serial::Write<Word> {}
+    pub trait Default: crate::nb::serial::Write {}
 
-    impl<S, Word> crate::blocking::serial::Write<Word> for S
+    impl<S> crate::blocking::serial::Write for S
     where
-        S: Default<Word>,
-        Word: Clone,
+        S: Default,
+        S::Word: Clone,
     {
+        type Word = S::Word;
         type Error = S::Error;
 
-        fn write(&mut self, buffer: &[Word]) -> Result<(), Self::Error> {
+        fn write(&mut self, buffer: &[Self::Word]) -> Result<(), Self::Error> {
             for word in buffer {
                 nb::block!(self.write(word.clone()))?;
             }
diff --git a/src/blocking/spi.rs b/src/blocking/spi.rs
index 571f7b32a..8c54d40af 100644
--- a/src/blocking/spi.rs
+++ b/src/blocking/spi.rs
@@ -1,48 +1,64 @@
 //! Blocking SPI API
 
 /// Blocking transfer
-pub trait Transfer<W> {
+pub trait Transfer {
+    /// Word type
+    type Word;
+
     /// Error type
     type Error;
 
     /// Writes `words` to the slave. Returns the `words` received from the slave
-    fn transfer<'w>(&mut self, words: &'w mut [W]) -> Result<&'w [W], Self::Error>;
+    fn transfer<'w>(
+        &mut self,
+        words: &'w mut [Self::Word],
+    ) -> Result<&'w [Self::Word], Self::Error>;
 }
 
 /// Blocking write
-pub trait Write<W> {
+pub trait Write {
+    /// Word type
+    type Word;
+
     /// Error type
     type Error;
 
     /// Writes `words` to the slave, ignoring all the incoming words
-    fn write(&mut self, words: &[W]) -> Result<(), Self::Error>;
+    fn write(&mut self, words: &[Self::Word]) -> Result<(), Self::Error>;
 }
 
 /// Blocking write (iterator version)
-pub trait WriteIter<W> {
+pub trait WriteIter {
+    /// Word type
+    type Word;
+
     /// Error type
     type Error;
 
     /// Writes `words` to the slave, ignoring all the incoming words
     fn write_iter<WI>(&mut self, words: WI) -> Result<(), Self::Error>
     where
-        WI: IntoIterator<Item = W>;
+        WI: IntoIterator<Item = Self::Word>;
 }
 
 /// Blocking transfer
 pub mod transfer {
     /// Default implementation of `blocking::spi::Transfer<W>` for implementers of
     /// `nonblocking::spi::FullDuplex<W>`
-    pub trait Default<W>: crate::nb::spi::FullDuplex<W> {}
+    pub trait Default: crate::nb::spi::FullDuplex {}
 
-    impl<W, S> crate::blocking::spi::Transfer<W> for S
+    impl<S> crate::blocking::spi::Transfer for S
     where
-        S: Default<W>,
-        W: Clone,
+        S: Default,
+        S::Word: Clone,
     {
+        type Word = S::Word;
         type Error = S::Error;
 
-        fn transfer<'w>(&mut self, words: &'w mut [W]) -> Result<&'w [W], S::Error> {
+        fn transfer<'w>(
+            &mut self,
+            words: &'w mut [Self::Word],
+        ) -> Result<&'w [Self::Word], S::Error> {
             for word in words.iter_mut() {
                 nb::block!(self.write(word.clone()))?;
                 *word = nb::block!(self.read())?;
@@ -57,16 +73,17 @@ pub mod transfer {
 pub mod write {
     /// Default implementation of `blocking::spi::Write<W>` for implementers
     /// of `nonblocking::spi::FullDuplex<W>`
-    pub trait Default<W>: crate::nb::spi::FullDuplex<W> {}
+    pub trait Default: crate::nb::spi::FullDuplex {}
 
-    impl<W, S> crate::blocking::spi::Write<W> for S
+    impl<S> crate::blocking::spi::Write for S
     where
-        S: Default<W>,
-        W: Clone,
+        S: Default,
+        S::Word: Clone,
     {
+        type Word = S::Word;
         type Error = S::Error;
 
-        fn write(&mut self, words: &[W]) -> Result<(), S::Error> {
+        fn write(&mut self, words: &[Self::Word]) -> Result<(), S::Error> {
             for word in words {
                 nb::block!(self.write(word.clone()))?;
                 nb::block!(self.read())?;
@@ -81,18 +98,19 @@ pub mod write {
 pub mod write_iter {
     /// Default implementation of `blocking::spi::WriteIter<W>` for implementers of
     /// `nonblocking::spi::FullDuplex<W>`
-    pub trait Default<W>: crate::nb::spi::FullDuplex<W> {}
+    pub trait Default: crate::nb::spi::FullDuplex {}
 
-    impl<W, S> crate::blocking::spi::WriteIter<W> for S
+    impl<S> crate::blocking::spi::WriteIter for S
     where
-        S: Default<W>,
-        W: Clone,
+        S: Default,
+        S::Word: Clone,
     {
+        type Word = S::Word;
         type Error = S::Error;
 
         fn write_iter<WI>(&mut self, words: WI) -> Result<(), S::Error>
         where
-            WI: IntoIterator<Item = W>,
+            WI: IntoIterator<Item = Self::Word>,
         {
             for word in words.into_iter() {
                 nb::block!(self.write(word.clone()))?;
@@ -117,12 +135,16 @@ pub enum Operation<'a, W: 'static> {
 
 /// Transactional trait allows multiple actions to be executed
 /// as part of a single SPI transaction
-pub trait Transactional<W: 'static> {
+pub trait Transactional {
+    /// Word type
+    type Word: 'static;
+
     /// Associated error type
     type Error;
 
     /// Execute the provided transactions
-    fn exec<'a>(&mut self, operations: &mut [Operation<'a, W>]) -> Result<(), Self::Error>;
+    fn exec<'a>(&mut self, operations: &mut [Operation<'a, Self::Word>])
+        -> Result<(), Self::Error>;
 }
 
 /// Blocking transactional impl over spi::Write and spi::Transfer
@@ -131,13 +153,14 @@ pub mod transactional {
 
     /// Default implementation of `blocking::spi::Transactional<W>` for implementers of
     /// `spi::Write<W>` and `spi::Transfer<W>`
-    pub trait Default<W>: Write<W> + Transfer<W> {}
+    pub trait Default: Write + Transfer {}
 
-    impl<W: 'static, E, S> super::Transactional<W> for S
+    impl<W: 'static, E, S> super::Transactional for S
     where
-        S: self::Default<W> + Write<W, Error = E> + Transfer<W, Error = E>,
+        S: self::Default + Write<Word = W, Error = E> + Transfer<Word = W, Error = E>,
         W: Copy + Clone,
     {
+        type Word = W;
         type Error = E;
 
         fn exec<'a>(&mut self, operations: &mut [super::Operation<'a, W>]) -> Result<(), E> {
diff --git a/src/fmt.rs b/src/fmt.rs
index 81e23cef5..55b63dfe5 100644
--- a/src/fmt.rs
+++ b/src/fmt.rs
@@ -3,7 +3,7 @@
 //! TODO write example of usage
 use core::fmt::{Result, Write};
 
-impl<Word, Error> Write for dyn crate::nb::serial::Write<Word, Error = Error> + '_
+impl<Word, Error> Write for dyn crate::nb::serial::Write<Word = Word, Error = Error> + '_
 where
     Word: From<u8>,
 {
diff --git a/src/lib.rs b/src/lib.rs
index 1dbb6dd49..1a0541cd1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -248,7 +248,7 @@
 //!
 //! fn write_all<S>(serial: &mut S, buffer: &[u8]) -> Result<(), S::Error>
 //! where
-//!     S: hal::nb::serial::Write<u8>
+//!     S: hal::nb::serial::Write<Word = u8>
 //! {
 //!     for &byte in buffer {
 //!         block!(serial.write(byte))?;
@@ -283,7 +283,7 @@
 //! ) -> Result<u8, Error<S::Error, T::Error>>
 //! where
 //!     T: hal::nb::timer::CountDown<Error = ()>,
-//!     S: hal::nb::serial::Read<u8>,
+//!     S: hal::nb::serial::Read<Word = u8>,
 //! {
 //!     timer.start(timeout).map_err(Error::TimedOut)?;
 //!
@@ -326,7 +326,7 @@
 //!
 //! fn flush<S>(serial: &mut S, cb: &mut CircularBuffer)
 //! where
-//!     S: hal::nb::serial::Write<u8, Error = Infallible>,
+//!     S: hal::nb::serial::Write<Word = u8, Error = Infallible>,
 //! {
 //!     loop {
 //!         if let Some(byte) = cb.peek() {
@@ -390,7 +390,8 @@
 //! #     fn deref_mut(&mut self) -> &mut T { self.0 }
 //! # }
 //! # struct Serial1;
-//! # impl hal::nb::serial::Write<u8> for Serial1 {
+//! # impl hal::nb::serial::Write for Serial1 {
+//! #   type Word = u8;
 //! #   type Error = Infallible;
 //! #   fn write(&mut self, _: u8) -> nb::Result<(), Infallible> { Err(::nb::Error::WouldBlock) }
 //! #   fn flush(&mut self) -> nb::Result<(), Infallible> { Err(::nb::Error::WouldBlock) }
diff --git a/src/nb/adc.rs b/src/nb/adc.rs
index 17de484dd..752e059db 100644
--- a/src/nb/adc.rs
+++ b/src/nb/adc.rs
@@ -64,23 +64,26 @@ pub trait Channel<ADC> {
 /// #     pub fn do_conversion(&mut self, chan: u8) -> u16 { 0xAA55_u16 }
 /// # }
 ///
-/// impl<WORD, PIN> OneShot<MyAdc, WORD, PIN> for MyAdc
+/// impl<PIN> OneShot<MyAdc, PIN> for MyAdc
 /// where
-///    WORD: From<u16>,
 ///    PIN: Channel<MyAdc, ID=u8>,
 /// {
+///    type Word = u16;
 ///    type Error = ();
 ///
-///    fn read(&mut self, pin: &mut PIN) -> nb::Result<WORD, Self::Error> {
+///    fn read(&mut self, pin: &mut PIN) -> nb::Result<Self::Word, Self::Error> {
 ///        let chan = 1 << pin.channel();
 ///        self.power_up();
 ///        let result = self.do_conversion(chan);
 ///        self.power_down();
-///        Ok(result.into())
+///        Ok(result)
 ///    }
 /// }
 /// ```
-pub trait OneShot<ADC, Word, Pin: Channel<ADC>> {
+pub trait OneShot<ADC, Pin: Channel<ADC>> {
+    /// Word type
+    type Word;
+
     /// Error type returned by ADC methods
     type Error;
 
@@ -88,5 +91,5 @@ pub trait OneShot<ADC, Word, Pin: Channel<ADC>> {
     ///
     /// This method takes a `Pin` reference, as it is expected that the ADC will be able to sample
     /// whatever channel underlies the pin.
-    fn read(&mut self, pin: &mut Pin) -> nb::Result<Word, Self::Error>;
+    fn read(&mut self, pin: &mut Pin) -> nb::Result<Self::Word, Self::Error>;
 }
diff --git a/src/nb/serial.rs b/src/nb/serial.rs
index 407e75300..7a3acca1b 100644
--- a/src/nb/serial.rs
+++ b/src/nb/serial.rs
@@ -4,21 +4,27 @@
 ///
 /// Some serial interfaces support different data sizes (8 bits, 9 bits, etc.);
 /// This can be encoded in this trait via the `Word` type parameter.
-pub trait Read<Word> {
+pub trait Read {
+    /// Word type
+    type Word;
+
     /// Read error
     type Error;
 
     /// Reads a single word from the serial interface
-    fn read(&mut self) -> nb::Result<Word, Self::Error>;
+    fn read(&mut self) -> nb::Result<Self::Word, Self::Error>;
 }
 
 /// Write half of a serial interface
-pub trait Write<Word> {
+pub trait Write {
+    /// Word type
+    type Word;
+
     /// Write error
     type Error;
 
     /// Writes a single word to the serial interface
-    fn write(&mut self, word: Word) -> nb::Result<(), Self::Error>;
+    fn write(&mut self, word: Self::Word) -> nb::Result<(), Self::Error>;
 
     /// Ensures that none of the previously written words are still buffered
     fn flush(&mut self) -> nb::Result<(), Self::Error>;
diff --git a/src/nb/spi.rs b/src/nb/spi.rs
index 6eb7fc233..7b9b8b3ad 100644
--- a/src/nb/spi.rs
+++ b/src/nb/spi.rs
@@ -13,10 +13,10 @@
 ///
 /// - Data is only guaranteed to be clocked out when the `read` call succeeds.
 /// The slave select line shouldn't be released before that.
-///
-/// - Some SPIs can work with 8-bit *and* 16-bit words. You can overload this trait with different
-/// `Word` types to allow operation in both modes.
-pub trait FullDuplex<Word> {
+pub trait FullDuplex {
+    /// Word type
+    type Word;
+
     /// An enumeration of SPI errors
     type Error;
 
@@ -24,10 +24,10 @@ pub trait FullDuplex<Word> {
     ///
     /// **NOTE** A word must be sent to the slave before attempting to call this
     /// method.
-    fn read(&mut self) -> nb::Result<Word, Self::Error>;
+    fn read(&mut self) -> nb::Result<Self::Word, Self::Error>;
 
     /// Writes a word to the slave
-    fn write(&mut self, word: Word) -> nb::Result<(), Self::Error>;
+    fn write(&mut self, word: Self::Word) -> nb::Result<(), Self::Error>;
 }
 
 /// Clock polarity