Ppc isa expansion

Amstrad PPC 512/640 — ISA Expansion Board

An open-hardware KiCad 8 design for an external-mount, internally-powered 3-slot XT-class (8-bit) ISA expansion board for the Amstrad PPC 512 and PPC 640 portable PCs.

The PPC is the 1988-era Amstrad luggable that ships with a CMOS-level expansion connector (DB25 + DB37) on its back. Amstrad sold an external "Expansion Box" that was meant to power the PPC and add peripheral slots. This project inverts the original topology: it takes power from the PPC's own PSU and gives you three standard XT 8-bit ISA slots in a compact board that clips onto the back of the machine via the two DB connectors — ready to host modern flash-based peripherals (XT-IDE, floppy emulators, network cards, etc.).

Gallery

The board has been fabricated and tested in a real Amstrad PPC 640 — booting DOS from a CompactFlash card via an XT-IDE controller. Photos below are of the assembled board in service.

Board mated to the PPC's DB25 + DB37 expansion port.	Top-down view showing the three ISA slots fanning out the back.
XT-IDE card with CompactFlash plugged into the centre slot.	The PPC 640 booting and running Test Drive from the CF card.

Repository layout

amstrad_isa/
├── README.md                  — this file
├── LICENSE                    — MIT
├── .gitignore                 — KiCad / Python / OS cruft
├── kicad/
│   ├── ppc-isa-expansion.kicad_pro
│   ├── ppc-isa-expansion.kicad_sch
│   ├── ppc-isa-expansion.kicad_pcb
│   ├── sym-lib-table          — project-local symbol libraries
│   ├── fp-lib-table           — project-local footprint libraries
│   └── ppc-isa.pretty/        — custom ISA 8-bit slot footprint
├── scripts/
│   ├── generate_schematic.py  — regenerates the schematic from tables
│   ├── generate_pcb.py        — regenerates the PCB skeleton
│   └── generate_bom.py        — emits docs/BOM.csv
├── fab/                       — ready-to-order gerbers + JLCPCB zip
├── docs/
│   ├── design_notes.md        — the *why* behind the schematic choices
│   ├── BOM.csv                — bill of materials
│   └── Amstrad_PPC_Technical_Reference_Manual.pdf
└── photos/                    — build & in-machine reference shots

I just want a board — no KiCad

If you don't want to install KiCad, the fab/ folder contains a ready-to-order gerber set straight from the committed .kicad_pcb.

1. Download fab/ppc-isa-expansion-gerbers.zip (no need to extract it).
2. Go to your favourite board house — JLCPCB, PCBWay, OSH Park and Aisler all accept this format unchanged.
3. Upload the zip. The defaults are fine: 2 layers, 1.6 mm FR-4, HASL or ENIG finish, any colour. Quantity 5 is usually the minimum and runs ~$5 + shipping.
4. Order, wait, populate from docs/BOM.csv.

The gerbers in fab/ always match the committed .kicad_pcb. If you fork and re-route, re-plot from KiCad and replace the contents of fab/.

Build from source (with KiCad)

git clone git@github.com:hustav/amstrad_isa.git
cd amstrad_isa

# Optional: regenerate the schematic / PCB from the Python source of truth
python3 scripts/generate_schematic.py
python3 scripts/generate_pcb.py

# Open the project
kicad kicad/ppc-isa-expansion.kicad_pro

The .kicad_sch and .kicad_pcb files were initially generated by the scripts in scripts/ — those scripts remain the source of truth for the netlist. The current .kicad_pcb has been routed by hand on top of that skeleton, so re-running generate_pcb.py would overwrite the routing. If you need to change the netlist, regenerate the skeleton and then redo the affected traces.

Key design choices

Full rationale lives in docs/design_notes.md.

Power topology — important caveat

The Amstrad PPC Technical Reference Manual (§1.18) states that the original Expansion Box is intended to supply power to the PPC, not draw from it. Connector B pin 20 is an EXT PWR input to the PPC's regulator.

This design reverses that flow — all four rails (+5 V, +12 V, −5 V, −12 V) are drawn from the PPC's expansion connector:

• +5 V from connector A pin 1 and connector B pin 37
• +12 V from connector B pin 36
• −5 V from connector B pin 17
• −12 V from connector B pin 18

Pin 20 (EXT PWR into the PPC) is left floating — voltage is never injected back into the PPC.

Safe for modern peripherals. An original floppy or 10 MB Winchester drew 5–10 W. A flash-based XT-IDE with a CF card draws ~100–200 mA on +5 V (0.5–1 W). Three flash peripherals are comfortably within the headroom the original PSU left for the Expansion Box port.

Not safe for original drives. If you try to use the original floppy or HDD controllers through this board, the PPC's PSU may brown out. In that case, build an externally-powered (ATX) variant instead.

Amstrad expansion pinout (Tech Ref §1.18)

Connector A (DB25 male on the board)

Mostly the address bus.

Connector B (DB37 male on the board)

Data bus, IRQs, DMA, control signals, power.

The full Amstrad PPC Technical Reference Manual is included in docs/ for reference.

Credits and prior art

This design builds on two community projects, both of which are externally-mounted boards that hang off the PPC's DB25 + DB37 connectors:

• João (enide.net) — original internally-powered design. Provided the mechanical approach and power topology. Only the gerbers were available (the project is currently offline), so the schematic was reverse- engineered from those files and cross-referenced against the Retrotheory design below.
• Retrotheory — amstradppc_expansion — ATX-powered variant. Provided the full schematic used as the electrical reference (74HC244 pinouts, the BEAT LED divider using a 74HC74, etc.).

Many thanks to both for sharing their work — without them this design would not exist.

License

Released under the MIT License. See LICENSE.