The ACSI2STM is an open source hard drive emulator designed for Atari ST computers, enabling the use of SD cards as storage devices. Powered by an STM32 microcontroller, it bridges the Atari’s ACSI port with modern SD cards, providing a cost-effective, reliable, and versatile solution for expanding storage on vintage Atari systems.

NEW! The SidecarTridge vision of the ACSI2STM

After extensive testing of the original ACSI2STM device, SidecarTridge has introduced an enhanced version with several key improvements:

• Upgraded 4-Layer PCB Design: This new design ensures optimal performance, even in older and noisier computer systems, by reducing issues like crosstalk and electrical interference.
• Premium microSD Card Slots: Utilizing the same high-quality slots as the SidecarTridge Multi-device, these are more robust and feature a built-in eject mechanism, facilitating easy insertion and removal of microSD cards.
• Optimized Crystal Oscillator Circuit: Adjustments in the capacitors of the crystal oscillator circuit have been made to enhance performance and stability. This modification addresses a flaw in the original design that could cause not working or prolonged boot times.

The new board design is slightly larger than the original ACSI2STM with this very distinctive castle shape, which is why it is called the “Castillian” ACSI2STM board. The new design is fully compatible with the original ACSI2STM firmware and retains all the features and functionality of the original device.

Key Features:

• Broad Compatibility: Supports Atari models such as 520 STF, 1040 STE, Mega ST, and Mega STE.

• GemDrive Mode: Offers seamless access to SD cards formatted with FAT16, FAT32, or ExFAT. This mode eliminates the need for additional drivers, making it easy to transfer files between your Atari and modern PCs.

• ACSI Mode: Emulates traditional ACSI hard drives and supports multiple partitions. This mode requires Atari-compatible hard disk drivers, offering enhanced compatibility with legacy software.

• Real-Time Clock (RTC): Includes UltraSatan-compatible RTC functionality, enabling accurate timekeeping on the Atari. A 3V lithium battery (CR2032 not included) is required for this feature.

• Firmware Upgradeable: The ACSI2STM firmware can be updated directly from the Atari, ensuring compatibility with future enhancements and bug fixes.

Place it inside your Megas: The Internal Riser Boards Option

Traditionally, this device connects externally via the ACSI port. We've developed two new riser boards that enable the internal installation of the ACSI2STM device within Atari Mega ST and Mega STE computers. This enhancement allows users to integrate the ACSI2STM seamlessly into their systems, eliminating the need for external connections and external powering and preserving the original aesthetics of the computer.

Benefits of Internal Installation:

• Internal Power Supply: No more wires to power your external device.
• Preserved Aesthetics: Maintains the original look of your Atari by keeping the ACSI2STM device concealed within the case.
• Reduced Wear: Minimizes wear on external ports and connectors by eliminating the need for constant plugging and unplugging.
• Space Efficiency: Frees up workspace by removing external devices and cables.

Kits Available

ACSI2STM Compact Kit

When purchasing the ACSI2STM kit, you’ll receive:

• Assembled PCB: A PCB with all components soldered and tested, including the DB-19 connector for the Atari ACSI port.
• Expansion Connector: A DB-20 connector to expand the ACSI port to Satan Disk and other devices. (Note: This connector is not soldered.)
• Firmware: Pre-installed latest stable firmware.

User-Supplied Items:

• Power Cable: A USB-C cable to power the ACSI2STM.
• Storage Media: An SD, SDHC, or SDXC card to store files. They must be formatted in FAT16, FAT32, or ExFAT for GemDrive mode or with Atari-compatible hard disk drivers for ACSI mode as described in the documentation.
• Compatible Computer: A functional Atari ST/MegaST/STE/MegaSTE/TT computer with an ACSI port.

Internal Riser Board for Mega STE + ACSI2STM Compact Kit

This kit includes:

• ACSI2STM Compact Kit: As detailed above.
• Mega STE Riser Board: Specifically designed for Mega STE.
• Pre-soldered 30-pin female connector.
• Pre-soldered 20-pin female connector.
• Pre-soldered USB-A power-only female connector.
• Power Cable: USB-A to USB-C cable (length varies between 10 cm and 15 cm, depending on availability).

Internal Riser Board for Mega ST + ACSI2STM Compact Kit

This kit includes:

• ACSI2STM Compact Kit: As detailed above.
• Mega ST Riser Board: Specifically designed for Mega ST.
• Pre-soldered 24-pin female connector.
• Pre-soldered 20-pin female connector.
• Pre-soldered USB-A power-only female connector.
• Two pre-soldered male pins for 5V power connection.
• Additional Connector: 20 cm female-to-female Dupont red connector.
• Power Cable: USB-A to USB-C cable (length varies between 10 cm and 15 cm, depending on availability).

Installation

The ACSI2STM is already pre-assembled and embeds the latest firmware, making it ready for use out of the box. The only steps required are to prepare an SD card and connect to your Atari system:

3. SD Card Preparation

• For GemDrive Mode: Format the SD card with FAT16, FAT32, or ExFAT to allow the Atari to access files directly without additional drivers.
• For ACSI Mode: Create disk images or partitions compatible with Atari’s hard disk drivers for legacy software.

4. Operation

• Insert the prepared SD cards into the slots.
• Connect the ACSI2STM to the Atari’s ACSI port.
• Power the ACSI2STM using a USB-C cable (not included).
• Power on the system. The Atari should detect the SD card as a hard drive, ready for file storage and retrieval.

This product is intended for users familiar with basic embedded systems and vintage computer hardware. While we offer support for hardware setup and firmware installation, the firmware is provided as-is. It is actively and continuously developed, and we encourage users to contribute by reporting bugs and suggesting features on the GitHub repository.