The SidecarTridge 256KB Decoder + TOS Emulator Combo lets a Mega ST transparently boot 192 KB and 256 KB TOS images, including STe and Mega STe builds, without touching the original ROM sockets and without soldering on the 68000. The decoder seats in the MEGABUS connector and links to the SidecarTridge TOS Emulator carrier (rev4+) through a 6-pin flat cable. From the Atari’s point of view, it just sees the ROM bus respond as expected.
Combo kit from €57 plus taxes. Ships from Spain. Mega ST only.
from €57 plus taxes
Already own a SidecarTridge TOS Emulator with the rev4+ Mega ST carrier? Get in touch for an upgrade bundle.
The decoder seats in the Mega ST bus connector. No 68000 desolder work, no permanent modifications.
Generates the missing address and CE signals so the emulator maps the $E00000 range exactly like a Mega STe.
Loads TOS 1.00 to 1.04, KAOS, TOS 2.06, SuperTOS 2.06, custom TOS 2.16 and EmuTOS 192 KB and 256 KB. TOS 1.06, 1.62 and 2.05 decode correctly but still do not run on Mega ST hardware.
The kit ships with the matching SidecarTridge TOS Emulator carrier for Mega ST plus the 6-pin interconnect cable.
Works alongside the stock Atari Blitter mezzanine that most Mega ST units carry. No desoldering required.
Designed around the RP2350-powered SidecarTridge TOS Emulator and its USB and SWITCHER workflow for loading and switching ROM sets.
The Mega ST never officially received the later 256 KB TOS builds. With this combo you can:
Step-by-step photos and the troubleshooting checklist live in the hardware installation guide and the quickstart.
| Mega ST motherboard | Carrier board | Status |
|---|---|---|
| C100167-001 Rev. 4.02 | Rev 4.0 SidecarTridge carrier | Supported |
| C100167-001 Rev. B2 | Rev 4.0 SidecarTridge carrier | Supported |
| C100167-001 Rev. 5.02 | Rev 4.0 SidecarTridge carrier | Supported |
| C100501-001 (2 ROMs) | Rev 4.0 SidecarTridge carrier | Supported |
| C103277 Rev 2.22 | Rev 4.0 SidecarTridge carrier | Supported |
| C103544-001 (2 ROMs) | Rev 4.0 SidecarTridge carrier | Supported |
Not sure which board you have? Open the case and check the silkscreen on the centre-bottom of the motherboard. The full breakdown lives in the SidecarTridge TOS buying guide.
No. This combo is Mega ST only. ST, STM, STF and STFM versions that required soldering onto the 68000 are discontinued. If you have a non-Mega ST, look at the SidecarTridge TOS Emulator instead.
Yes. The solderless decoder leaves the CPU area untouched, so the original Atari Blitter daughterboard can stay in place.
The combo is designed and supported on Atari Mega ST computers in their original stock configuration. The standard Atari Blitter patch is the only supported modification. Any other change (memory expansions, CPU accelerators, custom logic replacements, bodge wires, aftermarket ROM adapters) is out of scope and not covered by warranty. If your Mega ST is modified, please contact us before ordering.
No. The decoder board plugs into MEGABUS and the carrier sits in the ROM sockets. The 6-pin flat cable handles the rest.
Yes, if you enjoy tinkering with your Mega ST and you are comfortable opening the case once to seat the decoder and route a flat cable. It is a homebrew product, built for hobbyists who want to run STe-class TOS images on a Mega ST without permanent modifications. It is not a sealed appliance.
TOS 1.00, 1.02, 1.04, KAOS 1.4, TOS 2.06, SuperTOS 2.06, custom TOS 2.16, plus EmuTOS 192 KB and 256 KB. TOS 1.06, 1.62 and 2.05 still do not run on Mega ST hardware, even though they decode correctly through the 256KB Decoder.
Yes. The decoder board is now sold on its own.
Firmware downloads and the SWITCHER app are on the SidecarTridge TOS download page. EmuTOS lives on the EmuTOS project site. TOS is copyrighted material, so you should own a legal copy before using it with the SidecarTridge TOS Emulator.
Access to our products and community spaces requires basic respect. We have zero tolerance for harassment, personal attacks, abusive behaviour or defamatory content toward our team or community. The principle is simple: don’t be abusive. If that principle is violated, access is revoked. We build for people who enjoy experimenting, not for people creating hostility.
This product has been assessed for European (CE) and UK (UKCA) conformity. Official Declarations of Conformity and EMC Assessment reports for the decoder board and the combined kit:
