Using Stephen Leary’s open-source TF534r2c accelerator in an Atari 520ST

Although this card is considered unsupported and obsolete, I did have good success with it in my Atari.

Your mileage may vary!




The official channels for TF534 information and firmwares:
Terriblefire Forum:
Terriblefire GitHub:


Go to the Terriblefire GitHub for official firmware!

While the official firmware works, at present it does not support FastRAM or the IDE interface on Atari computers.
I have developed an unofficial Atari specific firmware that can be downloaded from here:

Changes are:

  • Made onboard ram available as TT-RAM at location 0x01000000
  • IDE interface working on Atari
  • Fixed Blitter related timing issue

The firmware builds for the TF530r3 as well and while I think it should work I cannot say for sure since I don’t have that board.

This is unofficial firmware – use at your own risk!
The rest of the information on this page assumes you are using this unofficial firmware.


I have a rather lengthy thread on the Exxos forum starting with building the board and gradually getting more and more stuff to fit the Atari better:


You need to be running a TOS version that supports the 030 processor.
TOS 2.06 or EmuTOS (256KB version) does the trick just fine.

EmuTOS is open-source and available here:
I recommend running with cache disabled when using TOS 2.06

Of course, you will likely need some modification to your Atari to make it able to accept 256KB ROMS. There appear to be different solutions out there, including information on how to build your own so I won’t recommend anything specific. I am using my own Blitter expansion board for this.
Alternatively, boot from some 192KB rom and load 2.06 or EmuTOS from disk and into RAM.


IDE Interface:
The IDE interface on the TF534 is byte-swapped compared to a standard Atari IDE interface.
TOS-only partitioned drives will need a twisted cable in order to “untwist” it back to Atari standard.
PC-compatible drives, which normally requires a “twisted cable” will probably work with a normal cable.

(TOS 2.06 only) Solder a wire from INT2 on the TF534 to ASCI pin 10 on the Atari motherboard, as usual with add-on IDE interfaces for Atari.


Running TOS and programs from FastRam (TT-RAM / AltRam) is crucial for getting performance because access to normal ST-RAM is held back by the 8Mhz system bus!

I have developed a program called “maprom” which will copy the contents of your roms to FastRam and configure the MMU so it executes from there.
Since TOS 2.06 can not automatically detect and install TT-RAM this program sorts this out as well.
MAPROM.PRG should be the first program in your AUTO folder.

Grab it from here:

There are different programs available to control if applications should load/allocate from fastram. I am using Georg Wagner’s flagsett program (download:


The blitter can not blit to/from fastram, and if it tries to do so you will get unexpected results and often crashes.
EmuTOS disables the blitter by default if it detects TT-RAM so you are safe using EmuTOS. However, TOS 2.06 does not and will crash quite quickly when running from FastRam.

If you have a Blitter installed, you could either just remove it or run my “blitfix” helper program.
This program attempts to allow blitter usage when possible while preventing it for blits outside of 24bit address space. While mainly for TOS 2.06, it is still useful when running EmuTOS since it will allow some more safe programs to use the blitter.
Blitfix should run after Maprom in your AUTO folder.

Grab it from the same place as maprom:


TF53x optimized EmuTOS:

Official EmuTOS works just fine, but this one adds a nice speed boost by letting it know about FastRam at compile time. It will also use the blitter when possible, even if FastRam is present.

English and German ROM images:


If you cannot use 256KB roms you could burn this 192KB boot rom ( and load the full EmuTOS from disk (
emutosuk.prg / emutosde.prg must be the first item in your auto folder, and don’t use maprom.prg.

The CPU is soldered to the motherboard in the 520ST so I had to desolder it and replace it with a socket. Multiple sockets actually, to build enough height for clearing the external floppy connector.

These devices work fine:

  • External floppy drive
  • Gotek
  • Ultrasatan (except for real time clock)
  • Parcp-USB

These devices does not work:

  • NetUsbee


Some benchmarks. CPU is running at 40Mhz.

Elite Frontier:


IDE interface:




Custom TF53x optimized EmuTOS:



Official EmuTOS 0.9.12:


TOS 2.06: