Apple II FPGA

[Stephen Edwards] had some time one Christmas. So he took a DE2 FPGA board and using VHDL built a pretty faithful reproduction of an Apple II+ computer. He took advantage of VHDL modules for the 6502 CPU and PS/2 keyboard, and focused more on the video hardware and disk emulation.

According to [Stephen], you can think of the Apple II as a video display that happens to have a computer in it. The master clock is a multiple of the color burst frequency, and the timing was all geared around video generation. [Stephen’s] implementation mimics the timing, although using more modern FPGA-appropriate methods.

The FPGA also has a read-only disk emulator. The image resides on an SD card and an SPI interface loads it into memory as required.

The DE2 board isn’t the cheapest around, although if you are a student you can get a break (in the neighbourhood of $200 instead of $400). They are so frequently used in schools though, that you can often pick one up for a good bit less on the used market. Also, there are plenty of cheaper boards with the same Altera FPGA that should be fairly straightforward enough to use.

[Stephen] notes that the FPGA version takes less power than a real Apple II+ and much less than a PC emulating one, although — as he notes — that’s hardly fair since the PC has a lot of overhead that has nothing to do with the emulation.

Of course, you can emulate the same type of machine on smaller hardware. We’ve even seen one based on an AVR processor.

Filed under: classic hacks, FPGA

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