Pre-power Checks & Bring-up

Pre-power sanity checks

1. Verify all 6 pull-up resistors: each is 10 kΩ from a 65C02 control pin to +3.3 V (R1–R6, see Wiring).

2. Verify RAM OE# (pin 22) → +3.3 V, not GND.

3. Verify chip orientations: both the 65C02 and RAM have notches at the top. Reversed orientation usually shorts VCC to GND instantly.

4. Continuity-check the shared bus wires. A0 should beep between 65C02 pin 9, Pico pin 1, and RAM pin 10. Repeat for each address and data line.

5. Check no short between the +3.3 V rail and GND rail.

6. Power the breadboard (external 3.3 V). Measure 3.3 V at 65C02 pin 8 and RAM pin 28. Do not connect external 3.3 V to Pico VSYS yet.

7. Flash piclone.uf2, plug in USB (Pico only), tie Pico GND to breadboard GND.

Bring-up sequence

1. Wire per Wiring, flash piclone.uf2, connect USB (Pico) + external 3.3 V (breadboard), common GND.

2. Set up host tools: install Romulan: cd ~/Downloads/romulan && uv sync.

3. Dumb-ROM test (no upload needed after a fresh boot): plug in USB, the built-in demo starts automatically and the CPU runs at 1 kHz. Observe it:

   cd ~/Downloads/romulan
   uv run python -c "
   from romulan.hardware_api import open_hardware_api
   with open_hardware_api() as api:
       api.monitor(enable=True)
       input('Press Enter to stop...')
       api.monitor(enable=False)   # before upload or read capture
   "
   

   Or capture structured bus data (built-in ROM ends in STP): uv run romulan hardware capture --max-cycles 500 --port /dev/ttyACM0.

4. Full program test:

   cd ~/Downloads/romulan
   uv run romulan program.txt --build --upload
   uv run romulan hardware capture --max-cycles 500 --port /dev/ttyACM0
   

5. RAM writes (optional): a program that STAs to $0200 (or $4000) can be observed via read / monitor. With OE# tied high the AS6C62256-55PCN never drives the bus, so LDA from RAM returns floating garbage. The built-in demo only writes to RAM.