The default configuration resembles an expanded Nascom 2 machine. Several ROM sockets can be operated as either ROM or RAM; special modes such as FDD, CP/M and BLS Pascal selectively change individual regions.
Base configuration
| Address range | Type | Size | Purpose |
|---|---|---|---|
$0000–$07FF |
ROM | 2 KiB | NAS-SYS 3 monitor |
$0800–$0BFF |
RAM | 1 KiB | Screen memory |
$0C00–$0FFF |
RAM | 1 KiB | Workspace used by various programs |
$1000–$AFFF |
RAM | 40 KiB | Program memory |
$B000–$B7FF |
ROM/RAM | 2 KiB | Toolkit |
$B800–$BFFF |
ROM/RAM | 2 KiB | NASPEN |
$C000–$C3FF |
ROM/RAM | 1 KiB | SUPERDEBUG |
$C400–$CFFF |
ROM/RAM | 3 KiB | NAS-DIS |
$D000–$DFFF |
ROM/RAM | 4 KiB | ZEAP 2.1 or NAS-DOS |
$E000–$FFFF |
ROM | 8 KiB | Microsoft BASIC |
Switchable operating modes
FDD and NAS-DOS
When the FDD function is enabled, NAS-DOS is mapped to $D000–$DFFF. The WD1793-compatible controller occupies ports $E0–$E5.
CP/M
CP/M mode automatically enables floppy support and switches the configurable ROM sockets to RAM. On reset, the 2 KiB boot ROM is visible at $F000–$F7FF and mirrored at the reset vector. The lower region is subsequently switched to shadow RAM.
BLS Pascal
Pascal mode maps a 12 KiB ROM to $A000–$CFFF. BASIC and other expansion ROMs are hidden, while $E000–$FFFF becomes writable RAM.
Notes for software
Programs should not assume that all expansion ROMs are visible at the same time. For portable NAS-SYS programs, RAM starting at $1000 is the natural choice. Operating modes and extensions should be detected before direct access to their ports, or enabled explicitly in the configuration.