ROM 4X and 5X are enhanced firmwares for the Apple //c and Apple IIc Plus.

Main features:

• Initializes memory expansion card without erasing it if it already contains a boot sector. This is intended for battery-backed memory expansions made by A2Heaven.
• Boot menu via CTRL+CLOSED-APPLE+RESET or CTRL+OPTION+RESET.
  • Allows dropping into the monitor immediately.
  • Allows clearing memory expansion card.
  • Allows launching diagnostics.
  • Allows selecting boot device.
    • 4X: Allows booting external 5.25 drive if disk supports it.
• 4X: With battery-backed RAMdisk, can configure default boot option.
• 5X: Replaces accelerator firmware.
  • CTRL+ESC+RESET toggles accelerator speed and persists across ordinary resets.
  • CTRL+TAB+RESET brings up a menu that lets you set accelerator state and some option.

In development:

• 5X - default boot option configuration like 4X, enhanced to set default accelerator state as well.

See ROM 4X and 5X on GitHub.

• 5X: The Merlin Fix Release
• 4X: The XModem-CRC Release
• The "binary" release
• (4X only) Boot Configuration Beta
• 2017-04-08 Release
• r20170208

In addition to the source code, GitHub releases starting October 2017 will have a “binary” release attached that includes binary patches and a patching script to apply them to a source ROM.