A 6502 Home-Brew Computer

Thanks to a burgeoning interest in electronics, I’ve become very interested in designing and building my own computer. I chose the 6502 out of familiarity and nostalgia. It was at the heart of my two favorite computers, the Commodore 64 (in a slightly modified version called the 6510) and the Apple ][. It’s a favorite of hobbyists, and there’s a ton of software targeted to it. Plus, it’s just very easy to design around.

Form Factor

  • Composed of two half-eurocard (80mm x 100mm) boards; one CPU and memory, one I/O. The design is constrained to such a small area because of the tool I’ve decided to use for PCB layout, CadSoft Eagle freeware version.
  • Fully buffered bus available on each stack, for easy expansion.
  • Boards are connected using standard 0.1” (2.54mm) SIP headers, à-la Arduino shields

CPU

  • Synertek SY6502B.
  • 1MHz Crystal Oscillator (The CPU is capable of running at 3MHz, but I only had a 1MHz 6551 on hand).

Memory

  • 32KB NEC µPD43256AC-10L SRAM (32K x 8).
  • 32KB ST 27C512 UV EPROM (64K x 8. Only the lower 16K is used), with a simple monitor program and 6502 Enhanced Basic.
  • Simple 74HC00 or 4000 series address decoding glue logic.

IO

  • Rockwell R6522A VIA — two 8-bit parallel I/O lines.
  • Rockwell R6551 ACIA — one serial I/O line, 50 to 19,200 baud.
  • MAX232 RS-232 voltage converter.
  • 1.8432 crystal.

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