Hackaday Prize 2022: Reuse these DIP chips to create a 1980s-style single board computer
With the massive chip shortage still delaying shipments of new components, now might be a good time to walk around your lab and inspect those piles of chips you think “might come in handy one day.” Chances are you’ll find a good stack of 74xx-series logic, once ubiquitous but now mostly obsolete thanks to powerful microcontrollers and FPGAs. It would be a shame to let them go to waste, so why not use them to make a neat 1980s-style computer?
With this idea in mind, [Anders Nielsen] designed the ABN6502: a single board computer based on the venerable 6502 processor, but with relatively modern interfaces like a VGA monitor output, a PS/2 keyboard connector and even a wireless module to simplify firmware downloads from a PC. A design requirement was to minimize the number of new components needed; the average hacker interested in building the ABN6502 will likely have plenty of chips lying around their workshop somewhere.
The parts list reads like a typical BOM for a 6502-based computer, but provides great flexibility to allow parts substitution. For the processor, the classic NMOS 6502 as well as the modern CMOS-based 65C02 are supported, along with their companion 6522 chip which provides I/O ports and timers. A ROM socket can contain modern, fast flash chips or traditional, but slow UV-erasable EPROMs.
Instead of using DRAM chips with their complicated refresh requirements, [Anders] opted for 32 KB of SRAM to implement main memory; unaffordable in the 80s but readily available today. Standard 74xx series logic chips glue all the components together, again with multiple options to add or remove features depending on user preference. Pin headers highlight I/O ports for easy connection to external devices.
The ABN6502’s software library is currently limited to a bootloader, but a full development toolchain based on the CC65 compiler should make it easy to develop all kinds of programs on this platform. We’ve already featured the intelligent wireless ROM flashing system, along with a demo of the 6502 driving RGB LEDs.
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