ZigZagJoe's Vintage

ISP-SIMM ROM for Macintosh

ISP-SIMM is a ROM module I designed in Dec 2023 for all models of 68K macintosh with a ROM SIMM. It is intended to support rapid development of ROM code and other bare-metal development on Macintoshes. With an integrated programmer, there is no need to remove the module from the logic board in order to program a new image.

In a matter of seconds a new image can be programmed and booted with no physical intervention required, and you don't even need to turn the system off! These have been instrumental in my hardware development and directly led to both the 30Video and NuCF PDS cards, among others.

Features

Universal ROM SIMM: Supports Macintosh II and Quadras!
16MB in two 8MB banks. Active bank selected by switch on module. JST-SH Header for remote switch.
USB Mass storage programming support via UF2 format
Optional RESET output for automatic reboot after programming is complete
USB -> Serial functionality

UF2 Mass Storage Programming

No drivers or software required! The SIMM shows up as a USB mass storage device within your OS of choice. You too can flash ROMs from your clamshell iBook! (yes, I tested!)
Simply drag a UF2 file to or from the drive to write a new image, or read back.
Powershell and python scripts to convert UF2 supplied on module.
8MB image read in 20 seconds, writes in 50 seconds.

Serial port

A built-in serial header can be connected to a macintosh serial port when combined with level shifter daughterboard and DIY cable. This is intended to support debugging operations without an additional USB to serial adapter. Selectable baud rate.

Notes

It is normal for the ISP-SIMM "drive" to briefly disappear and reappear after writing an image. Some OS may complain that the drive was improperly ejected. This can be ignored.
Do not use this module with any 3rd party ROM programmer devices. It may cause damage to the module or the programmer.
Apple ROM Flash utility and any other software flash utilities are not supported.
Certain Mac II-series machines may require a jumper to be set to disable onboard ROMs. Quadras will automatically have their ROMs disabled.

Readme
Firmware and other resources