ACA500plus Firmware

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The ACA500plus features an 8MByte flash ROM with a rich set of software: The menu system, Kickstart ROMs, Action Replay ROMs, HRTmon, and the OS3.1 install files. On this page, you will mainly find software updates for the menu system, but also recovery files for other parts of the flash ROM.

Menu update

The menu update file is provided as zip archive, because you will most likely unpack it on a Windows-, Linux-, or Mac-PC. Unpack the archive to the root directory of a PC-formatted CF card.

Download: Menu system V0.99

Insert that card into the AUX slot of your ACA500plus, then launch the menu. Press F8 and F to launch the flasher, which will read the update file from the AUX card. Follow the instructions on screen to install the update. If something does not work right away, you may need to reset the computer to launch the flash process.

The unpacked file is an ADF image that can also be written to a floppy disk. You will only need to do this if the flash ROM has been garbled - in that case, the bootable floppy will serve as a recovery-disk.

HRTmon update

This is an update that you will only need once in order to use HRTmon with any version of the menu system that you install *after* the delivery version. The actual HRTmon remains the same (and will never be overwritten with a menu software update), but the checksum and header are adapted to what the new menu system software expects. This update can ONLY be used with the flash updater from the menu. It cannot be written as ADF to a recovery disk, despite its file name.

Please note that the WHDload commands of HRTmon currently do not work. This is in the works and will be fixed with a future update.

Download: HRTmon

CAUTION: This one is only good for menu systems up to V0.97. For 0.99, please use the intermediate version of april 3rd. That one also makes WHDload commands work.

intermediate test version

This intermediate version may contain new bugs or incompatibilities that we haven't found yet. It already has a revision bump to V0.98, but you should also write down the datestamp that is displayed while you're flashing. We will need that with a possible bug report!

This update comes in two files and must be installed in two flash sessions. One is the menu, the other is the new version of HRTmon. Please do not mix versions! HRTmon and it's updated functions will only work after both update files have been flashed.

Download 1: Menu V0.98 (April 3rd, 2017) Download 2: HRTmon (April 3rd, 2017)


  • HRTMon now uses ACA500plus Action Replay emulation hardware to save and restore chip registers
  • HRTMon is now compatible with whdload commands
  • HRTMon PAL/NTSC mode now follows configured ACA500plus PAL/NTSC mode
  • acaflashrom command now has a "LIST" option. Caution: If ROMs are not re-flashed, size information is not available.
  • floppy detection now stops all drive motors and de-selects all drives before attempting to recognize drives.
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