diff --git a/README.md b/README.md
index 8f04f8e..a0527d7 100644
--- a/README.md
+++ b/README.md
@@ -37,6 +37,7 @@
 
 - [Easy 6502](https://skilldrick.github.io/easy6502/)
 - [Annotated Snake6502](https://gist.github.com/wkjagt/9043907)
+- [Ultimate Commodore 64 Reference - 6502](https://www.pagetable.com/c64ref/6502/)
 
 ## Colophon
 
diff --git a/firepower-cpu/src/main/scala/com/htmlism/firepower/cpu/CpuState.scala b/firepower-cpu/src/main/scala/com/htmlism/firepower/cpu/CpuState.scala
new file mode 100644
index 0000000..2542736
--- /dev/null
+++ b/firepower-cpu/src/main/scala/com/htmlism/firepower/cpu/CpuState.scala
@@ -0,0 +1,35 @@
+package com.htmlism.firepower.cpu
+
+case class CpuState(
+    accumulator: UByte,
+    xRegister: UByte,
+    yRegister: UByte,
+    stackPointer: UByte,
+    programCounterLo: UByte,
+    programCounterHi: UByte,
+    negative: Boolean,
+    overflow: Boolean,
+    break: Boolean,
+    decimal: Boolean,
+    interruptsDisabled: Boolean,
+    zero: Boolean,
+    carry: Boolean
+)
+
+object CpuState:
+  val empty: CpuState =
+    CpuState(
+      accumulator        = UByte(0),
+      xRegister          = UByte(0),
+      yRegister          = UByte(0),
+      stackPointer       = UByte(0),
+      programCounterLo   = UByte(0),
+      programCounterHi   = UByte(0),
+      negative           = false,
+      overflow           = false,
+      break              = false,
+      decimal            = false,
+      interruptsDisabled = false,
+      zero               = false,
+      carry              = false
+    )
diff --git a/firepower-cpu/src/main/scala/com/htmlism/firepower/cpu/UByte.scala b/firepower-cpu/src/main/scala/com/htmlism/firepower/cpu/UByte.scala
new file mode 100644
index 0000000..8d38a53
--- /dev/null
+++ b/firepower-cpu/src/main/scala/com/htmlism/firepower/cpu/UByte.scala
@@ -0,0 +1,15 @@
+package com.htmlism.firepower.cpu
+
+opaque type UByte =
+  Byte
+
+extension (b: UByte)
+  def inc: UByte =
+    ((b & 0xff) + 1).toByte
+
+  def dec: UByte =
+    ((b & 0xff) - 1).toByte
+
+object UByte:
+  def apply(n: Int): UByte =
+    n.toByte