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TeensyROM | Colossal Capabilities for the C64

Updated: Mar 22

Unleash Retro Magic: Travis Smith's TeensyROM Elevates the Commodore 64!

Travis Smith, a devoted fan of vintage computing, has innovated a cutting-edge accessory for the beloved Commodore 64 and its successor, the Commodore 128. Dubbed the TeensyROM, this cartridge is powered by Teensy 4.1 and offers a plethora of functionalities in one sleek package. The TeensyROM acts as a ROM emulator, rapid loader, MIDI Host and Device, as well as an internet interface for both the Commodore 64 and 128 models. Smith emphasizes that his creation is compatible with various C64 and C128 machine variants, supporting both NTSC and PAL systems.

In its most basic form, the TeensyROM serves as a tool to load cartridge ROM images onto an authentic Commodore 64 or compatible device. These images can be loaded from the Teensy's internal flash storage or from external sources such as microSD cards or USB storage devices (up to 32GB) where you can load .crt, .prg and .p00 files. Notably, it can also load program files extremely swiftly compared to traditional Commodore storage devices like the 1541 floppy drive or Datasette cassette tape deck.

Beyond these capabilities, the TeensyROM offers additional features that elevate its utility. It functions as a MIDI input/output interface, enabling users to harness the iconic MOS Technology 6581 Sound Interface Device (SID) chip through a USB MIDI keyboard or drive external MIDI equipment directly from the Commodore 64. Moreover, users can stream MIDI- or SID-formatted files from a modern PC to experience them on original hardware.

Furthermore, this innovative gadget provides internet connectivity via an Ethernet port that mimics a Swiftlink cartridge with an attached 38.4kbps modem for online access. With comprehensive MIDI capabilities and Ethernet support integrated into the cartridge design, users have access to a wealth of versatile functionalities.

Explaining his choice of using Teensy 4.1 for this project, Smith highlights its advanced external interface capabilities such as USB Host & Device support alongside SD Card and Ethernet compatibility. Leveraging its numerous IO pins for direct interfacing allows for extensive software-defined functionalities within the device.

The open-source nature of TeensyROM on GitHub under MIT license offers full transparency with access to source code, hardware design files, and even printable case designs for enthusiasts interested in exploring further customization options or building their own.

For those less inclined towards DIY projects but eager to experience the benefits of TeensyROM first-hand, fully assembled units are available for purchase on


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