diff --git a/src/main/kotlin/razorvine/c64emu/CpuIoPort.kt b/src/main/kotlin/razorvine/c64emu/CpuIoPort.kt
index bdb2147..12a9934 100644
--- a/src/main/kotlin/razorvine/c64emu/CpuIoPort.kt
+++ b/src/main/kotlin/razorvine/c64emu/CpuIoPort.kt
@@ -7,11 +7,12 @@ import razorvine.ksim65.components.UByte
 /**
  * The 6510's IO port located at $00/$01
  * Controlling the memory layout, and cassette port (not processed at all).
+ *
  */
 class CpuIoPort(val cpu: Cpu6502) : MemMappedComponent(0x0000, 0x0001) {
 
     private var dataDirections: Int = 0
-    private var ioPort: Int = 0
+    private var ioPort: Int = 0xff
     var loram: Boolean = false  // Bit 0: LORAM signal.  Selects ROM or RAM at 40960 ($A000).  1=BASIC, 0=RAM
         private set
     var hiram: Boolean = false  // Bit 1: HIRAM signal.  Selects ROM or RAM at 57344 ($E000).  1=Kernal, 0=RAM
@@ -20,7 +21,11 @@ class CpuIoPort(val cpu: Cpu6502) : MemMappedComponent(0x0000, 0x0001) {
         private set
 
     override fun clock() { }
-    override fun reset() { }
+    override fun reset() {
+        dataDirections = 0xff
+        ioPort = 0xff
+        determineRoms()
+    }
 
     override operator fun get(offset: Int): UByte {
         return if(offset==0) dataDirections.toShort() else {
diff --git a/src/main/kotlin/razorvine/c64emu/GUI.kt b/src/main/kotlin/razorvine/c64emu/GUI.kt
index a479d2f..561b79a 100644
--- a/src/main/kotlin/razorvine/c64emu/GUI.kt
+++ b/src/main/kotlin/razorvine/c64emu/GUI.kt
@@ -53,7 +53,7 @@ object ScreenDefs {
     val colorPalette = Palette()
 }
 
-class MainC64Window(title: String, chargen: Rom, val ram: MemoryComponent, val cpu: Cpu6502, val keypressCia: Cia) :
+class MainC64Window(title: String, chargen: Rom, val ram: MemoryComponent, val cpu: Cpu6502, private val keypressCia: Cia) :
         JFrame(title), KeyListener {
     init {
         defaultCloseOperation = EXIT_ON_CLOSE
diff --git a/src/main/kotlin/razorvine/c64emu/c64Main.kt b/src/main/kotlin/razorvine/c64emu/c64Main.kt
index 1678def..9f8ccda 100644
--- a/src/main/kotlin/razorvine/c64emu/c64Main.kt
+++ b/src/main/kotlin/razorvine/c64emu/c64Main.kt
@@ -41,8 +41,14 @@ class C64Machine(title: String) : IVirtualMachine {
 
     override val cpu = Cpu6502()
     val cpuIoPort = CpuIoPort(cpu)
+
+    // This bus contains "mmu" logic to control the memory bank switching controlled by the 6510's io port in $00/$01.
+    // Therefore we provide it the various roms directly and not "connect" these to the bus in the default way.
     override val bus = Bus6510(cpuIoPort, chargenRom, basicRom, kernalRom)
+
+    // the C64 has 64KB of RAM.  Some of it may be banked out and replaced by ROM.
     val ram = Ram(0x0000, 0xffff)
+
     val vic = VicII(0xd000, 0xd3ff, cpu)
     val cia1 = Cia(1, 0xdc00, 0xdcff, cpu)
     val cia2 = Cia(2, 0xdd00, 0xddff, cpu)
@@ -57,13 +63,11 @@ class C64Machine(title: String) : IVirtualMachine {
         cpu.addBreakpoint(0xffd8, ::breakpointKernelSave)       // intercept SAVE subroutine in the kernal
         cpu.breakpointForBRK = ::breakpointBRK
 
-        bus += basicRom // TODO remove this
-        bus += kernalRom  // TODO remove this
         bus += vic
         bus += cia1
         bus += cia2
         bus += cpuIoPort
-        bus += ram
+        bus += ram      // note: the ROMs are mapped depending on the cpu's io port
         bus += cpu
         bus.reset()