LEGACY & BROWNFIELD · PROTOCOL COVERAGE
14 protocols·Serial to OPC UA·Read-only·No new hardware
You do not need to replace a 1995 Modbus PLC to put an AI agent on it. The same kernel that reads a 2025 OPC UA server reads the serial link on the machine next to it.
Read-only. Forge reads through standard industrial protocols. Nothing is written back. Your equipment is never at risk.
Around 70% of installed manufacturing equipment is 20+ years old. It is depreciated, it is running, and it is making money. The standard vendor answer — new controllers, new gateways, a capital project and an 18-month schedule — is why most brownfield AI programmes die in the budget meeting rather than the technical review.
But the equipment is not silent. A 1995 machine with a Modbus RTU serial link is already emitting everything an agent needs. Nobody translated it, because translating it was worth less than the integration cost. That calculation changes when the translation is a single API call.
Serial is not a second-class citizen here. Modbus RTU over RS-232 / RS-485 lands in exactly the same canonical schema as OPC UA, so a 1995 PLC and a 2025 controller produce comparable fields in the same response. The agent cannot tell which machine was older, and it should not have to.
Point Forge at the existing serial link, PLC register map, MTConnect agent or historian CSV export. No controller firmware changes, no new PLC logic, no downtime window.
Raw registers and coil addresses become named canonical fields. 40001 stops being a number and starts being spindle_speed_rpm.
Six read-time validators catch stuck sensors, dropouts and impossible rates of change. Legacy equipment produces more of all three, which is exactly why this layer exists.
REST or MCP. The same 32-tool surface serves the 1995 machine and the 2025 one.
| Raw source in | Canonical field out | Notes | |
|---|---|---|---|
| modbus rtu 40001: 3400 | → | spindle_speed_rpm: 3400 | holding register, RS-485 serial |
| modbus rtu 40012: 785 | → | spindle_temperature_c: 78.5 | scale factor resolved at map time |
| opc ua ns=2;s=Spindle.Speed | → | spindle_speed_rpm: 3400 | modern controller node |
| j1939 SPN 190: 1850 | → | engine_speed_rpm: 1850 | CAN bus, heavy vehicle |
The scale factor case is the one that quietly ruins retrofit projects. A register holding 785 for 78.5°C is correct in the PLC and catastrophic in an agent that reads it as 785°C. Unit and scale resolution is part of the mapping, not an exercise left to the reader.
Longer-form writing on industrial AI infrastructure by Foundry Labs.