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A Bit of Vectrex History
Mine Storm
Fortress of
Dark Tower

Vectrex Programmers Guide

Memory Map

The 68A09 can address memory between $0000 to $FFFF (65Kb).

The ports of the 6522 programmable interface adapter (PIA) have been mapped into the memory space beginning at $D000. A PIA port is selected by the setting of address bits 3 to 0 (the least significant address byte). The setting of address bits 11 to 4 (the two middle bytes) are ignored. As a result, $D12F, $D6AF or $DFFF is the same as $D00F - only bits 15 to 11 (which must be to a hex D) and bits 3 to 0 matter.

The Vectrex memory has been mapped as follows:

Address Range   Description
  $0000 - $7FFF   (32kb)     Reserved for game ROM   (read only)
  $C800 - $CBFF   (1kb)     Static RAM   (read or write)
        $C800 - $C87F   (128b)         Reserved for RUM
        $C880 - $CBFF   (896b)         Reserved for game logic
  $Dxx0 - $DxxF   (16b)     The Programmable Interface Adapter   (read or write)
  $E000 - $EFFF   (4kb)     Reserved for Mine Storm   (read only)
  $F000 - $FFFF   (4kb)     Reserved for the RUM   (read only)

The 68A09 has reserved the highest 16 bytes of memory for its various vectors:

Address Range   Description
  $FFF0 - $FFF1     Reserved
  $FFF2 - $FFF3     Vector to the Software Interrupt #3 (SWI3) Handler
  $FFF4 - $FFF5     Vector to the Software Interrupt #2 (SWI2) Handler
  $FFF6 - $FFF7     Vector to the Fast Interrupt Request (FIRQ) Handler
  $FFF8 - $FFF9     Vector to the Maskable Interrupt (IRQ) Handler
  $FFFA - $FFFB     Vector to the Software Interrupt (SWI) Handler
  $FFFC - $FFFD     Vector to the Non-Maskable Interrupt (NMI) Handler
  $FFFE - $FFFF     Reset Vector


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This page was last modified: 26 Feb 2021
By John Hall