Eight bits should be enough for anyone..
RSS icon Email icon Home icon
  • A Diagnostic ROM Image For The ZX Spectrum

    (Current version: 1.28 – Added NMI bus scanner).

    This is a ROM  image I originally made to help me diagnose faults I had in a Spectrum which had failed massively (dead ROM, bad memory, stuck keys etc). It is supplied with my own SMART Card but can be written to any suitable ROM replacement system.

    You can try this Diag ROM out with a Spectrum emulator program (EG: Fuse) by selecting it as the default .ROM, replacing the usual Sinclair one (most emus have this feature).

    RAM Tests:

    On reset, the Spectrum should beep once and show a title page. The border then goes yellow and the lower 16K of RAM is tested, this takes about 15 seconds and garbage appears on screen during the test – this is normal. If this test encounters bad RAM, an error message is shown, with the bad bits underlined. A list of the respective chips likely to be faulty in the Spectrum 48 (or 128) is also shown.

    In case the display is unreadable (or the Spectrum is not connected to a TV) the bad bits are also indicated by a sequence of 8 beeps (from bit 7 to bit 0) A high beep is a good bit, a low beep is a bad bit. The good/bad bit status is also indicated afterwards by stripes in the border, the topmost stripe being bit 7 (green=bit OK, red=bit bad). If the lower RAM is OK, then just 2 short beeps are heard.

    Next, the Upper 32KB of memory is tested (if fitted). This takes about 30 seconds and the border is magenta during this stage. Again, if there are problems an error message is shown and there are beeps to indicate the bad bits. If the upper RAM is OK, 3 short beeps are heard.

    Other Tests:

    If at least one RAM test completes successfully, the following extra tests can be run:

    1. keyboard + Kempston joystick
    2. IRQ test
    3. Speaker test
    4. Floating bus test
    5. Colour pattern test
    6. Sinclair ROM test
    7. Monitor EAR signal
    8. More RAM tests
    9. Spectrum 128 Tests

    Full documentation is in the .zip file

    Disclaimer: Hobby Project – Cannot guarantee bug-free! Use at your own risk..