Inventory the software-facing contract
- Identify serial, USB/HID, virtual COM or vendor-specific transport.
- Preserve DLLs, SDK headers, import units, calling conventions and driver versions.
- Map requests, responses, callbacks, Windows messages and device state transitions.
- Record polling intervals, timeouts, retries and thread ownership.
- Capture known-good workflows with timestamps and raw inputs/outputs where safe.
Do not perform device I/O on the UI thread merely because the original component allows it. Conversely, moving callbacks to a worker thread can break code that assumes VCL access occurs on the main thread.
Control modernization risk
| Compiler upgrade | Recheck pointer sizes, character encoding, records, callbacks and DLL signatures. |
|---|---|
| Device replacement | Compare command/state semantics, not just connector and nominal protocol. |
| Driver update | Measure enumeration, buffering, latency and event behavior. |
| API wrapper | Make ownership, cancellation, timeouts and error reporting explicit. |
Keep electrical testing and unsafe physical probing outside the application maintenance workflow. For industrial equipment, begin with documentation and passive evidence.
Use Delphi serial communication for COM-port design, barcode scanners, undocumented hardware protocols and the Delphi pillar.