Steve Chamberlin over at Big Mess o’Wires presents the Plus Too, a working hardware replica of the Macintosh Plus and Macintosh 512Ke computers.
The original Macs contained a Motorola 68000 CPU and about half a dozen major support chips, with all of the Mac-specific behaviors and OS routines defined in a 128K toolbox ROM. Plus Too uses an FPGA to model the Mac’s IWM (floppy controller), SCC (serial ports), VIA (general purpose I/O), mouse, and keyboard hardware. The toolbox ROM data was copied from my real Mac Plus (nicknamed “Lonely”) for use with Plus Too.
The project is built on an Altera DE-1 FPGA dev board and at this time implements only the absolute minimum of hardware necessary to boot the computer. The disk is read-only, and there is no keyboard, sound, SCSI, serial ports, or real-time clock. In the next version, Steve plans to use a custom built board and a real 68000 CPU, and add the physical connectors necessary to use a real Mac Plus mouse and keyboard if desired.
For all the details on this project, check out the Plus Too build log.