Modbus integration
Modbus is still the most common way to read energy meters, inverters, drives, small PLCs and environmental controllers. It is simple and widely supported, but it carries no units, names or timestamps. Most of the integration work is describing what each register means.
Variants and transport
Modbus TCP runs over Ethernet, normally on port 502, and addresses devices by IP and unit identifier. Modbus RTU runs over RS-485 serial lines, where several slaves share a bus and are addressed by slave ID with settings such as 9600 or 19200 baud, parity and stop bits. RTU devices are usually reached through a serial-to-Ethernet gateway, which also maps unit identifiers to bus addresses.
Prerequisites
- The manufacturer register map for the exact model and firmware version.
- Addressing details: IP and port, or gateway plus slave ID, and serial settings for RTU.
- Confirmation of whether the map is zero-based or one-based, and the word order for 32-bit values.
- Agreement with the site on polling intervals so control traffic is not disturbed.
- Network access restricted to the reading host; Modbus has no authentication of its own.
Reading registers
Holding registers are read with function code 03 and input registers with function code 04; coils and discrete inputs use 01 and 02. ALLINLET groups contiguous addresses into block reads to reduce round trips. A 16-bit register may hold a signed or unsigned integer, while two consecutive registers may hold a 32-bit integer or IEEE 754 float, with byte and word order varying by vendor.
Payload meaning
A raw value only becomes a measurement after scaling. A meter may report voltage as tenths of a volt, so 2315 means 231.5 V, and energy as a 32-bit counter in watt-hours that rolls over at its maximum. The mapping records data type, scale, offset, unit and whether the value is instantaneous or cumulative. Because Modbus provides no timestamp, the measurement time is the time the poll response was received, which is recorded honestly as such.
Limitations
- No security in the protocol: confidentiality and access control depend on network segmentation or a secure tunnel.
- Polling is sequential; long buses and short intervals cause timeouts.
- Exception responses such as illegal data address usually indicate a map or firmware mismatch.
- Writes are out of scope for the integration.
- Inclusion in the catalogue is not a claim that every device profile has been validated; each map is checked against live values.
Working with Edge
Register maps can be recorded in the Edge configuration registry and exported for use on a site gateway that publishes values onwards.
Further reading
Catalogue listings describe possible integration paths. Implementation and validation status is confirmed for each source during project scoping; no certification, service level or price is implied by this page.
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