ROMs¶

The Apple II system requires two ROM files, and can use a third:

ROM name	Chip	Purpose
`apple2`	`341-011`…`341-015` + `341-020`	Applesoft BASIC + Autostart Monitor, mapped at `$D000`–`$FFFF`
`chargen`	`341-0036`	Character generator — the 64 glyph bitmaps the rasterizer draws
`disk2` (optional)	`341-0027`	Disk II 16-sector boot ROM (P5), mapped at `$C600` while a disk is inserted

Without disk2 the machine is simply a diskless Apple II Plus; only booting disk images is unavailable.

Important

Apple II ROMs are copyrighted by Apple. You may need to own a real Apple II to use them.

Where to get them¶

The Avalonia app can download both ROMs for you — open the Apple II Configuration section in the sidebar, click Apple II config…, then Download ROMs. A licence acknowledgement is shown first. Alternatively, supply the files yourself.

The most actively maintained archive is the Asimov mirror, under emulators/rom_images/ — note that this is not under images/, which holds floppy disk images.

System ROM — apple.rom, a bare 12 KB $D000-$FFFF image. (apple_ii+_rom.zip and APPLE2_.ROM hold the same ROM in the 20 KB layout.)
Character generator — entry 3410036.BIN inside ROMS.ZIP, whose index (ROMS.ZIP.TXT) lists 341-0036 as the "][plus character ROM". No standalone II/II+ character generator dump is published at the top level of that directory, so the emulator extracts it from the archive by entry name — the archive holds 42 .bin files, so matching on extension alone would be ambiguous.
Disk II boot ROM — Apple Disk II 16 Sector Interface Card ROM P5 - 341-0027.bin-with-D4-D7 data bits swapped.bin. Note the long name: the plainly-named 341-0027 file next to it is a raw PROM dump with the D4–D7 data lines in hardware order, which the CPU cannot execute. The "swapped" variant is the one in CPU bit order, recognisable by starting with A2 20 A0 00.

Other sources include AppleWin's source tree and archive.org TOSEC firmware sets; MAME's apple2p set definition is the authoritative reference for per-chip file names and SHA-1s.

Accepted images¶

The loader accepts either layout and validates it by SHA-1:

Layout	Size	SHA-1
Trimmed `$D000`–`$FFFF`	12,288 bytes	`8c5ca0c39005dfb0898af2c0992f797cc77530c0`
Emulator-distribution `$B000`–`$FFFF`	20,480 bytes	`29a53f3bb158b160433369e8e4a1d7cd5bf68ac6`

In the larger layout the leading 8 KB is padding and the meaningless $C000–$CFFF I/O space; only the last 12 KB is loaded.

Six 2 KB per-chip dumps also circulate — 341-011-D0 through 341-015-F0 (Applesoft) plus 341-020-F8 (Autostart Monitor). Concatenate them into a single 12 KB image in address order before use.

The character generator¶

The 2513 character generator is a separate chip and is not part of the system ROM image. On real hardware it is wired to the video circuitry only — the CPU cannot read it — so the emulator holds it aside for the rasterizer rather than mapping it into the address space.

Layout	Size	SHA-1
`341-0036` dump	2,048 bytes	`f9d312f128c9557d9d6ac03bfad6c3ddf83e5659`

Only the leading 512 bytes carry unique data: 64 glyphs of 8 scan lines, 5 dots per line stored in bits 5–1 with the most significant bit leftmost. The remainder of the file repeats that block with bit 7 set and then duplicates both halves. The loader takes the leading 512 bytes.

The 64 glyphs are @ A–Z [ \ ] ^ _ followed by space ! " # … ? — uppercase only, which is why an Apple II Plus cannot display lowercase.

The Disk II boot ROM (optional)¶

Layout	Size	SHA-1
`341-0027` P5, CPU bit order	256 bytes	`d4181c9f046aafc3fb326b381baac809d9e38d16`

This is the controller card's boot PROM, mapped at $C600 while a disk is inserted. Only the 16-sector P5 (341-0027) is supported; the 13-sector 341-0009 boots the older DOS 3.2 format, which the drive emulation does not read.

Watch out for the two circulating dumps of this chip. The one named plainly 341-0027 is a raw PROM read with the D4–D7 data lines in hardware order and will not execute; the usable image is the one whose name ends "with D4-D7 data bits swapped", and it starts A2 20 A0 00 A2 03.

Where to put them¶

By default, desktop hosts look for Apple II ROMs in the shared user content directory:

macOS/Linux: ~/Documents/Highbyte/DotNet6502/roms/Apple2
Windows: %USERPROFILE%\Documents\Highbyte\DotNet6502\roms\Apple2

The directory and filenames can be changed in app settings. User changes saved by the apps are written to the host-specific appsettings.user.json overlay under the OS local application data directory, not beside the shipped executable. A shipped appsettings.json can still provide packaged defaults:

"Highbyte.DotNet6502.Apple2.Avalonia": {
  "SystemConfig": {
    "ROMDirectory": "",
    "ROMs": [
      { "Name": "apple2",  "File": "apple.rom" },
      { "Name": "chargen", "File": "3410036.BIN" },
      { "Name": "disk2",   "File": "Apple Disk II 16 Sector Interface Card ROM P5 - 341-0027.bin-with-D4-D7 data bits swapped.bin" }
    ]
  }
}

The browser-based apps store ROM files in browser local storage after upload.