Development log

From owner’s problem
to working module.

Port220 was built by Tom Radom, owner of Jaguar XJ220 chassis #50. What follows is the record: what was tried, what failed, and what the failures revealed. Seven months from first capture to first communication.

2021Ownership

Chassis #50 acquired

Chassis #50 at the Pebble Beach Concours d’Elegance — Pebble Beach, 2024

Chassis #50 on track at Circuit of the Americas — Circuit of the Americas

Jan 2026Acquisition

Original SPD-1039 and a period laptop

Communication with the car established within days using a modern operating system and a DB9-to-USB adapter. The module itself remained the obstacle.

Teardown rejected: the internals are potted in 1990s silicone, and opening it risked destroying an unobtainable part.

The original Zytek SPD-1039 factory service module with its loom and DB9 adapter — The original Zytek SPD-1039, with loom and DB9 adapter.

Feb 2026Capture

Logic analyzer on the line

An 8-channel logic analyzer and a DB9 bridge recorded traffic between laptop and module in PulseView, with the module left sealed.

FindingUART, with translation and inversion applied

PulseView capture showing decoded UART traffic across three channels — PulseView — ECU line, DB9 pin 2 and pin 3 decoded in parallel.

Eight-channel logic analyzer clipped to the diagnostic line — 8-channel, 24 MHz.

Feb – Mar 2026Protocol

Decode and design

Dynamic display and fault-clear sessions recorded at the car to resolve the full protocol. Schematic and PCB design self-taught in KiCad over the same period.

Late Mar 2026Fabrication

First boards submitted

Design submitted to PCBWay. Several revisions followed on their advice before anything was manufactured.

May 2026Revision C

First prototype — failed

Four-pin design. No communication, and a power conflict between the 12V rail fed from the vehicle and the 5V fed from the USB side.

Consequence12V pin and step-down network abandoned entirely

The Revision C prototype with its enclosure and USB serial board — Revision C field modified to Revision D.

31 Jul 2026Revision D

First communication

Three-wire design, powered entirely from USB, connected to chassis #50. Communication established with the Zytek ECU, stored faults read, and the check engine light cleared.

Interface5V UART · TX, RX, GND · USB bus-powered

Aug 2026Production

Revision F

FT232RNL bridge, TVS-clamped signal lines, sealed enclosure. Launcher built for Windows 11 and macOS, the macOS build signed and notarized. Schematic and bill of materials published in full.

Modules shipped to owners in the United Kingdom, continental Europe and the United States.

The production Port220 Service Module with cap and lead — Production Release A of the Port220 Service Module.

Sept 2026Android

Android support released

The launcher ported to Android, running the same DOSBox session and the same Zytek service aid as the desktop builds. Touch targets stand in for the function and arrow keys the DOS application expects.

A fully portable solution — the Service Module draws all the power it needs from the phone or tablet, so diagnostics run at the car with no laptop and no external power source.

PlatformsWindows · macOS · Android

The Port220 Service Module connected by USB-C to an Android phone running Command Module, with the ECU lead coiled alongside — Service Module connected, vehicle set to XJ220 — No laptop, no external power source — the Service Module runs from the phone.

Owner inquiry