A homebrewed Apple II clone. Read more on the blog post
- The CPU is a standard 65C02 running at near 1.024 MHz (the original Apple II ran at 1.023 for the 60 Hz models), after dividing the 4.096 MHz crystal by 4.
- The 12kB ROM image is placed on the 32k EEPROM. Becuase there's spare room on this chip a jumper allows for selecting the high or low half of the ROM chip, so I've placed Ardian Black's Deadtest program in there.
- 48kB of RAM is accomplised by using one and half 32kB SRAM chips. Figured this was easier to use matching chipd than it was to use a 32kb + 16kB chip.
- Address decoding works exactly like the real Apple II. This was mostly based on the schematics in Understanding The Apple II by Jim Sather.
- In Addition to the I/O slots, this has:
- Speaker: matching the genuine Apple II
- Game I/O: as the NE558 quad timer is hard to find, I've implemented this replacement using a pair of 556 chips.
- Keyboard: a Raspberry Pi Pico provides a modern USB interface but electrically it connects to the Apple II in the same way as the original ASCII keyboard did. The Pi can also generate a reset pulse when pressing Control + Print Screen, and also performs a power-on reset for the system. The firmware for this is in this project here.
- Graphics: there is absolutely no onboard hardware for displaying graphics. Instead you'll want to use an Apple VGA Card.
- Features deliberately missing:
- Expansion slots do not provide the DMA, USER 1 or 7M clock signals.
- The bus is not buffered: with a CMOS design this is less likely to be a problem (although no guarantees for interfacing with cards using 74LS logic).
- There is no cassette input or output.
- These are the Revision 1 files. Rev 0 was a smaller board with no 5V regulation, only 7 slots and 32k on board RAM. The plan had been to leave out slot 0 and work out how to make full use of a second 32k RAM chip to have the full 64k without needing a language card, however this almost doubled the amount of circuitry needed.
Combining the design of the Apple II with the ProFile hard disk, the case requires a bit of assembly:
- Print each piece with the flat side on the print bad (you could print the lid pieces as one if desired)
- Glue the "tongue" into the slot along the bottom inside edge of the front piece. This will locate into the notch inside the front of the base.
- Glue the top, front and sides together.
- For the light pipe it was filled with hot glue to create a diffused lense with the LED glued in behind.
- The base requires 8x M3 threaded inserts, 2 of which are for the back panel, the rest are the PCB mounts.
- The 20mm speaker can be taped into the round hole in the base.