The Modbus bridge - history

How the Modbus bridge came about. What it is and does is in A Modbus bridge. Newest first.

2026-10-01 - v1 built

Modbus TCP, the address in the endpoint and how to read it in channelInfo, change-only reporting with a deadband, queued writes, modbusStatus on a device that stops answering - the plugin in its own repo, corModbusBridge, tested against a Modbus device in the functests.

Channel parameters: from the endpoint string to channelInfo

A Channel had an endpoint, a kind and a direction. Modbus needs typing and scaling; the first version put them in the endpoint string, which made a scale factor part of the Channel's identity, and left every future transport (OPC-UA sampling, MQTT QoS and codec) to invent its own URL syntax. The endpoint became the address and channelInfo - key-value pairs, as receiverInfo - the rest, handed to the plugin by channelAddInfo (bridge ABI 9).

This settled the first of the design's open questions - "Mapping in the endpoint, or ...?" - decided: channelInfo.

Before any code - the proposal

modbus-bridge.md was originally written as a proposal, to decide the shape before any code.