diff --git a/cpu.go b/cpu.go
index 93ceef2..ccbbd17 100644
--- a/cpu.go
+++ b/cpu.go
@@ -15,10 +15,12 @@ type Cpu struct {
 }
 
 const (
+	ZeropageBase = 0x0000 // 0x0000-00FF Reserved for zeropage instructions
+	StackBase    = 0x0100 // 0x0100-01FF Reserved for stack
+
 	ResetVector = 0xFFFC // 0xFFFC-FFFD
 	IrqVector   = 0xFFFE // 0xFFFE-FFFF
 
-	StackBase = 0x0100 // One page 0x0100-01FF
 )
 
 // Create an new Cpu instance with the specified AddressBus
diff --git a/doc.go b/doc.go
new file mode 100644
index 0000000..d596848
--- /dev/null
+++ b/doc.go
@@ -0,0 +1,60 @@
+/*
+The i6502 package contains all the components needed to construct
+a working MOS 6502 emulated computer using different common parts,
+like the MOS 6502, WDC 65C02, VIA 6522 and ACIA 6551.
+
+The CPU is the core of the system. It features 8-bit registers and
+ALU, and can address 16-bit of memory. It features a 16-bit program
+counter (PC) that indicates where from memory the next instruction will
+be read.
+
+Besides the Cpu, there is also an AddressBus, which maps the 16-bit
+address space to different attached components that implement the Memory
+interface. Ram is one such component.
+
+Creating a new emulator is easy and straightforward. All that's required
+is a Cpu, and AddressBus and attached components.
+
+Example: create an emulator using the full 64kB address space for RAM
+
+    import "github.com/ariejan/i6502"
+
+    // Create Ram, 64kB in size
+    ram, err := i6502.NewRam(0x10000)
+
+    // Create the AddressBus
+    bus, err := i6502.NewAddressBus()
+
+    // And attach the Ram at 0x0000
+    bus.Attach(ram, 0x0000)
+
+    // Create the Cpu, with the AddressBus
+    cpu, err := i6502.NewCpu(bus)
+
+The hardware pins `IRQ` and `RESB` are implemented and mapped to
+the functions `Interrupt()` and `Reset()`.
+
+Running a program from RAM is possible by loading it into
+memory at the specified address. Note that this also sets the
+Program Counter to the beginning of the loaded program.
+
+Keep in mind that 0x00xx is reserved for Zeropage instructions and
+0x01xx is reserved for the stack.
+
+    import "io/ioutil"
+
+    program, err := ioutil.ReadFile(path)
+
+    // This will load the program (if it fits within memory)
+    // at 0x0200 and set cpu.PC to 0x0200 as well.
+    cpu.LoadProgram(program, 0x0200)
+
+Running a program is as easy as calling `cpu.Step()`, which will
+read and execute a single instruction.
+
+    go for {
+        cpu.Step()
+    }()
+
+*/
+package i6502