Description
The ISP-SIMM by ZigZagJoe is a USB-programmable ROM SIMM for classic Macintosh systems, including the SE/30, Macintosh II series, and compatible Quadra models. It replaces traditional ROM chips with a flexible solution for quickly testing, updating, or restoring system firmware.
The module features 16MB of flash storage split into two independent 8MB banks, selectable via a physical switch. This allows you to store and switch between two ROM images instantly.
An onboard RP2040 presents the SIMM as a USB drive, letting you flash ROM images by simply dragging and dropping UF2 files—no external programmer or drivers required. A built-in serial interface provides optional logging and control for advanced use.
Key Features
- Dual 8MB ROM banks (16MB total)
- USB drag-and-drop flashing (UF2)
- Onboard RP2040 programmer
- Hardware bank switch for instant ROM selection
- USB serial logging interface
- Optional RESET_OUT for automatic system reset
Ideal for ROM development, testing, and restoration, the ISP-SIMM simplifies working with classic Macintosh firmware.
Check out the setup guide here: https://zigzagjoe.com/ISP-SIMM.html
Read more about the ISP-SIMM’s functionality on the GitHub here: https://github.com/ZigZagJoe/ISP-SIMM_public/tree/main
Machines shipped with the OEM ROM on a SIMM, primarily the Macintosh IIfx, SE/30, and certain IIsi units—may experience fitment or reliability issues with the stock socket. In these cases, the pads may need to be “thickened” with solder to ensure a stable electrical connection.
Compatibility includes most Macintosh II and Quadra-class systems equipped with a SIMM socket. For Macintosh II models with ROMs soldered directly to the logic board, a jumper must be configured to disable the onboard ROMs.
