CRT Cellar

Salvaged screens, arcade relics and home-computer history, logged on tape.

STATUS ONLINE Posts: 50

Assembly Lessons From an Apple II Manual

Mara Kestrel 18-06-2026 9 Comments
Photo for Assembly Lessons From an Apple II Manual

The original Apple II reference manual teaches assembly the way the machine expects to be spoken to: through the built-in monitor, one hex byte at a time.

The first program

  • Enter the monitor with CALL -151.
  • Type the bytes that toggle the speaker in a loop.
  • Run it with G and listen to the click become a tone.

The manual assumes you are clever and curious. That is still the best way to write one.

Jonas Leclerc

Typing a program in by hand is slow, but you never forget what each byte does afterwards.

MA
MARA KESTREL AUTHOR
Member since 2016 6 posts

Tube technician with twenty years on broadcast monitors. Mara runs the Thursday CRT bench and still owns the degaussing coil she built in college.

COMMENTS

9 REPLIES
Sort:
  1. LE
    LENA VOSS 30-06-2026 @ 15:54

    Came for the repair, stayed for the tangent about the manual layout.

    1. VB
      VBLANK 01-07-2026 @ 10:42

      Rosin flux from a jar, cleaned with isopropyl straight after.

      1. JO
        JONAS LECLERC 03-07-2026 @ 18:59 MEMBER

        Rosin flux from a jar, cleaned with isopropyl straight after.

  2. JO
    JONAS LECLERC 03-07-2026 @ 08:22 MEMBER

    Nice work. For anyone reading: the service manual is on page 14 of the archive scans.

    1. VB
      VBLANK 07-07-2026 @ 12:05

      Six-month check is on the calendar.

  3. BI
    BITSHIFTER 04-07-2026 @ 07:19

    The sound on this one still gives me goosebumps.

    1. LO
      LOWRES_LARRY 05-07-2026 @ 22:29

      Thanks! The shield photo took about twenty attempts.

  4. PA
    PAL_OR_NTSC 04-07-2026 @ 23:59

    Honestly the composite version has a charm the RGB one lacks. Fight me.

  5. TO
    TOMASZ K. 08-07-2026 @ 22:41

    This is exactly the write-up I needed before opening mine. Bookmarked.

LEAVE A COMMENT