# ADAM Universal Interface (SPI) — Schematic Re-Capture

A KiCad-9 re-capture of Richard F. Drushel's hand-traced prototype schematic
(`serpar_working_bitmap2.tif`, 15 July 2005) for PCB X00257 REV 0.

## Files

    SPI_Schematic_Capture.html / .docx
        The authoritative transcription: complete component inventory, power
        rails, a block-by-block netlist, and the open questions that need a
        board trace to settle. Every line is evidence-tagged
        (CONFIRMED / INFERRED / OPEN). This is the document to read first and
        the reference a CAD re-draw works from.

    ADAM_Universal_Interface.kicad_sch
        A KiCad 9 schematic (format version 20241108). Every component is placed
        as a rectangle symbol with named, numbered pins, and connectivity is
        expressed through global net labels rather than drawn wires. This is the
        robust way to hand off a netlist: it opens cleanly and is electrically
        complete, and you re-arrange/re-wire it in Eeschema to taste.

    source_schematic.png
        The Drushel bitmap, converted from the original TIFF for reference.

    design_data.py, gen_capture_html.py, gen_kicad.py
        The single data model and the two generators, so the capture and the
        KiCad file stay in sync if anything is corrected.

## Opening the KiCad file

1. Open `ADAM_Universal_Interface.kicad_sch` in KiCad 9 Eeschema.
2. The symbols are self-contained scaffold parts (rectangles with the right
   pins) embedded in the file's `lib_symbols`, so it opens without needing any
   external library. Replace them with proper library parts (the real MC6801,
   SCN2661, 2114, MC1488/89, 74LS gates, etc.) as you formalise the drawing.
3. Run **Tools -> Annotate Schematic** and then **Inspect -> Electrical Rules
   Checker (ERC)**. The global labels carry the connectivity; matching label
   names are the same net.

## What's solid vs. what to verify

Solid (CONFIRMED): the MC6801 + SCN2661A + 2114 x2 core, the +5 V -> +/-12 V
DC-DC supply, the RS-232 level-shift to the DB-25, the AdamNet analog front end
around the LM339, the Centronics status/handshake inputs, the 4.9152 MHz baud
crystal, and the three-position mode switch.

Verify against the board (OPEN — see section 5 of the capture doc):
  - U3 identity/role: address latch (74LS373) vs. a parallel-data latch.
  - Exact decode part numbers (the LS09 / LS01 reads are lower-confidence).
  - Y1 (6801 main crystal) value — not legible on the 2005 scan.
  - The parallel data source (6801 GPIO port vs. memory-mapped latch).
  - The component-designation table in Drushel's title block — below the scan's
    legible resolution; a higher-DPI rescan of just that corner recovers the
    exact R/C values.
  - MC1488 / MC1489 exact markings.

## Why net-label connectivity

Hand-authoring fully-wired KiCad schematics is fragile — a single off-grid
endpoint breaks a net silently. Expressing connectivity through global labels on
short pin stubs is the format KiCad itself uses for cross-sheet nets; it is
exact, survives re-layout, and is the reliable way to deliver a machine-readable
schematic that opens on the first try. The trade-off is that the initial sheet
looks like a parts bin with labels rather than a tidy wired drawing — that's the
intended starting point for the hand re-draw.
