Editing Psion Organiser II (section)

=== Memory map ===

{| class="wikitable styled-table" style="width:85%; text-align:left;"
|+'''HD6303X memory map'''<ref name="tech2" />
! Range !! Assignment
|-
| <code>$8000–$FFFF</code> || External PROM — 8, 16 or 32 KB, filled from the top down
|-
| <code>$0400–$7FFF</code> || External RAM — 8, 16 or 31 KB, filled from <code>$2000</code> up (except the 31 KB option, from <code>$0400</code>)
|-
| <code>$0100–$03FF</code> || External I/O — the LCD and the control IC's latches
|-
| <code>$0000–$00FF</code> || Processor internal RAM and registers (192 bytes of RAM at <code>$0040–$00FF</code>, also retained when off)
|}

The memory-mapped I/O block is decoded in 64-byte pages, and every one of these is '''address-triggered''': any access at all, read or write, causes the event.<ref name="tech2" />

{| class="wikitable styled-table" style="width:70%; text-align:left;"
|+'''Memory-mapped I/O'''<ref name="tech2" />
! Range !! Function !! !! Range !! Function
|-
| <code>$0180–$01BF</code> || LCD ENABLE || || <code>$0300–$033F</code> || COUNTER RESET
|-
| <code>$01C0–$01FF</code> || SWITCH OFF || || <code>$0340–$037F</code> || COUNTER CLOCK
|-
| <code>$0200–$023F</code> || PULSE ENABLE || || <code>$0380–$03BF</code> || NMI ENABLE
|-
| <code>$0240–$027F</code> || PULSE DISABLE || || <code>$03C0–$03FF</code> || NMI DISABLE
|-
| <code>$0280–$02BF</code> || ALARM SET || || <code>$02C0–$02FF</code> || ALARM RESET
|}