6502 SBC Rev 2 — Breadboard to PCB
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Starting KiCad PCB Design
Patrick · Apr 1, 2026 4:45 PMCreated the schematic in KiCad. Used a 2-layer board design. Keeping it simple — all through-hole components for easy assembly.\n\nThe address decoding is clean: one 74HC00 gives me RAM, ROM, and I/O chip selects. Added test points on the address and data buses for debugging with a logic analyzer.
Serial Working at 19200 Baud
Patrick · Mar 22, 2026 10:15 AMWired up the MAX232 and got serial I/O working through the 65C22 VIA. Using a bit-banged software UART since this build doesn't have an ACIA chip.\n\nBaud rate is stable at 19200. Tested with PuTTY and minicom. The VIA timer interrupt handles the timing.
Breadboard Prototype Complete
Patrick · Mar 15, 2026 2:30 PMGot the 6502 running on a breadboard. Had a frustrating issue where the RAM chip was getting warm — turned out pin 20 (CE) was floating. Once I tied it to the address decoder output, everything worked.\n\nEhBASIC boots and I can type programs via the serial terminal. The reset circuit needed a 1uF cap instead of 100nF to get a clean startup.