LOGO! 8 and Modbus TCP: Connecting the Micro-PLC to SCADA and BMS
LOGO! 8 isn't just a relay replacement — its built-in Ethernet port speaks Modbus TCP, letting it read energy meters, feed data to an HMI, or report into a BMS without extra gateways. Here's how the integration actually works, and where it stops.
How we approach the integration
Define the role
Decide whether LOGO! 8 acts as Modbus TCP server (exposing its own I/O and flags to a SCADA or BMS) or client (polling meters and other slaves) — the two roles can run together on the same unit.
Map I/O and variables
Assign digital/analog I/O, markers and function block outputs to Modbus register addresses in LOGO! Soft Comfort, matching them against the master's or slave's register map before commissioning.
Connect meters, HMI and BMS
Poll energy meters as a Modbus TCP client, or let an HMI/BMS read LOGO!'s registers as a server — both over the same Ethernet port, alongside the built-in web server.
Harden the OT network
Put LOGO! on a segmented VLAN, restrict which hosts can reach its Modbus port, and disable services you don't use — basic hygiene for any Ethernet-connected controller.
What the integration actually covers
Both roles, one module
LOGO! 8 can poll other Modbus devices and expose its own registers at the same time, without an added gateway.
Client and server roles
Run LOGO! 8 as a Modbus TCP client to poll meters and sensors, and as a server so an HMI, SCADA or BMS can read and write its points — concurrently, on one Ethernet interface.
I/O and variable mapping
Digital and analog I/O, markers and function block outputs map to Modbus holding registers and coils inside LOGO! Soft Comfort, with the built-in simulator to check the mapping before deployment.
Energy meters over Modbus
Most Modbus TCP energy and power meters can be polled directly, feeding consumption data into LOGO!'s own logic or passed through to a BMS dashboard.
HMI, SCADA and BMS links
As a Modbus TCP server, LOGO! 8 fits into an existing SCADA or BMS point list alongside larger controllers, useful for a satellite panel that doesn't justify a full PLC.
Where LOGO! stops
It handles a handful of Modbus connections and a moderate point count well; for many I/O points, redundancy or complex sequencing, a full PLC is the more appropriate platform.
What we stock for this integration
Components for bringing LOGO! 8 onto a Modbus TCP network, ready to ship.
- LOGO! 8 base modules and expansion I/O
- Managed Ethernet switches for OT segmentation
- DIN-rail patch panels and network cabling
- Surge and network protection devices
- Technical guidance from our engineers
Frequently asked questions
Can LOGO! 8 be a Modbus TCP client and server at the same time?
Yes — the two roles run concurrently on the same Ethernet port, so LOGO! 8 can poll meters as a client while an HMI or BMS reads its registers as a server.
How is the register mapping actually done?
In LOGO! Soft Comfort, you assign I/O, markers and function block outputs to Modbus addresses, then verify the mapping against the master's or slave's documented register map before commissioning.
Can LOGO! 8 read a third-party energy meter directly?
In most cases yes, provided the meter offers a documented Modbus TCP register map — LOGO! 8 polls it as a client and can use the values in its own logic or forward them on.
When should we use a full PLC instead of LOGO! 8 for this?
Once the point count, number of Modbus connections or sequencing complexity grows past what a micro-PLC comfortably handles, or redundancy is required, a full PLC platform is the safer choice.
What's the minimum network hardening for a LOGO! 8 on Modbus TCP?
Segment it onto its own VLAN, limit which hosts can reach its Modbus and web-server ports, and disable services that aren't in use — the same baseline hygiene any Ethernet-connected controller needs.
Plan your LOGO! 8 integration with us
Talk to our engineers about I/O mapping, Modbus TCP connections and the components for your next OT integration.