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Quickstart - ND-120 on the MEGA65

Run the 1988 Norsk Data ND-120 minicomputer on a MEGA65 from a ready-built core file - no FPGA toolchain, no cables, no PC software. The core is the whole machine: the ND-120 CPU board with 4 MB of memory, a Tandberg TDV2200 terminal on the MEGA65's own keyboard and screen, and two floppy drives, two Winchester discs and a paper-tape reader served from image files on the SD card. It boots SINTRAN III from a Winchester image.

Status (02-SEP-2026): built and simulated, NOT YET RUN ON A MEGA65. Every part of this core has run on a DE10-Nano (MiSTer) or a Nexys 4 DDR or passes its testbench, but this combination has never met a real MEGA65. If you have one, you are the test - see "What to report" at the end. Keep a copy of your disc images.

What you need:

  • A MEGA65 (R3/R3A, or R4/R5/R6) and its keyboard and a monitor (VGA or HDMI - both work)
  • A micro-SD card, FAT32
  • The core file for YOUR board revision from the GitHub Release:
    • nd120_mega65_rev3_13MHz_115200.cor - R3 / R3A (most machines bought before 2024): main memory in the 8 MB HyperRAM, CPU at 13.33 MHz
    • nd120_mega65_r6_20MHz_115200.cor - R6 (machines shipped 2024 or later, serial numbers above 1000), also R4/R5: main memory in the 64 MB SDRAM, CPU at 20 MHz
  • A Winchester disc image with SINTRAN III (not part of the release - it is Norsk Data's software; the ND preservation community keeps images and ndtool builds and inspects them). Floppy and paper-tape images are optional.

The MEGA65 refuses a core built for another revision ("Core hardware model mismatch!"), so the filename's rev3/r6 must match your board. Not sure which you have: hold RESTORE for about 2 seconds (the freezer opens), press HELP - "MEGA65 MODEL" is on that screen.

1. Prepare the SD card

  1. Format the micro-SD as FAT32 (the internal or the external slot both work).
  2. Copy the .cor file onto it (anywhere).
  3. Make a folder /nd120 on the card and put your disc images in it (the Winchester image with SINTRAN III at least; floppy and tape images if you have them). Also copy nd120cfg into it - the 35-byte settings file from Verilog/fpga/mega65/sdcard/nd120/ in this repository. With it the menu settings survive a power cycle; without it they reset every time. Writes to the images go to the card, so keep a copy of your images.

2. Flash the core (standard MEGA65 procedure)

  1. Insert the card. Power on while holding NO SCROLL - the core menu appears.
  2. Press CTRL + a slot number (any slot except 0; keep slot 1 for the stock MEGA65 core), pick the .cor file.
  3. Do not reset or switch off until the confirmation message - flashing takes a minute or two.
  4. To run it: power on holding NO SCROLL and press the slot number. A plain power cycle returns to the stock core; nothing is permanent.

3. What you see, and how to boot

  1. The framework's welcome page. Press Space.
  2. A green 80x25 terminal with the power-on banner: ND-120 ..., a line with the git hash and build date, and a line saying MEGA65 R3 or MEGA65 R6 with the CPU clock and memory - that line identifies the build in any photo. Below the text: the operator panel (program level, lamps, MIPS).
  3. The case power LED is the CPU's verdict: amber while the CPU runs its self-test, green when it passed (the same meaning as the CPU board's own green lamp). Amber that never turns green means the CPU did not come up.
  4. Press RETURN. The microprogram answers with the OPCOM prompt. That is the no-disc smoke test: CPU, memory and console are alive.
  5. Press HELP - the menu. Under Drives, mount your Winchester image on Winch. 0 (and floppies / tape if you have them). Close the menu.
  6. At the OPCOM prompt type 20500& and RETURN. SINTRAN III boots from Winchester 0: first lines within about 30 seconds, then SINTRAN III RUNNING and the login. Floppy 0 boots with 1560&.

The keyboard types what the MEGA65 keycaps say, shifted symbols included. INST/DEL is Backspace, CLR/HOME is Home, the cursor keys and F1-F8 send the TDV2200 codes, CAPS LOCK latches as the keycap does. RUN/STOP is EXIT (the TDV2200's SLUTT key - how you leave a SINTRAN program); ALT+X is the same key. The menu also sets the text colour (green/amber/white/cyan), the operator panel on/off, the CPU cache on/off and the HDMI mode. What each field of the operator panel means: Verilog/fpga/mega65/docs/01-using-the-core.md, "Reading the operator panel".

Troubleshooting

Symptom Meaning
Flash menu says "Core hardware model mismatch!" wrong revision's file - see above
Black screen, but HELP still opens the menu the framework is alive, the ND-120 terminal is not - report it
Banner shows, RETURN gives no OPCOM prompt, power LED stays amber the CPU did not pass its self-test - report it with the banner line
OPCOM answers, 20500& prints nothing no image mounted on Winch. 0, or the image is not a bootable SINTRAN disc
SINTRAN boots but feels slow disc images are served by the framework's small firmware CPU reading the SD card; SINTRAN paging speed on that path is unmeasured - report timings

What to report (the first testers)

  1. A photo of the screen with the banner, and one after 20500& (the SINTRAN start-up text, or whatever happened instead).
  2. The power LED colour after a few seconds (amber / green).
  3. Which output: VGA or HDMI.
  4. Your MEGA65 model.

If the screen stays black: does the HELP menu still appear? That tells us whether the framework is alive and only the ND-120 is dark, or the whole core failed. Please do not spend time debugging - what you saw is the data. The build's own facts (timing, what is proven where) are in Verilog/fpga/mega65/docs/00-plan.md; the port itself in Verilog/fpga/mega65/README.md.