Connecting Two Siemens LOGO! 8 Modules via Ethernet in LOGO!Soft Comfort

Siemens LOGO! 8 (order group 6ED1052-xxx08-0BAx) base modules include an integrated Ethernet interface that allows multiple units to exchange digital and analog process data over a standard LAN. Unlike earlier LOGO! generations that required the LOGO! DM8 expansion modules, the LOGO! 8 family (0BA8 standard, 0BA8 FS:04, and later revisions) supports up to 16 network connections per base module between a remote client and a server. This reference documents the practical procedure for creating those network links inside LOGO!Soft Comfort (V8.0 through V8.3), explains the meaning of the colored connector lines (blue, green, gray) shown in the network project view, and clarifies when a manual line must be drawn between modules before logic is programmed.

Overview: How LOGO! 8 Peer-to-Peer Networking Works

LOGO! 8 base modules communicate over Ethernet using the proprietary LOGO! connection protocol that rides on top of standard TCP/IP. Each base module operates as both a server (publishing its own digital and analog I/O to the network) and a client (subscribing to the I/O of other units). In a network project, a single LOGO! can simultaneously serve several peer modules, and a single network connection is identified by the server-side connector (input or output of the server LOGO!) and the client-side connector (input or output of the client LOGO!).

The maximum number of supported network connections depends on the firmware generation of the LOGO! 8 base module:

LOGO!Soft Comfort V8.2 and later allow you to set up an entire LAN project containing several LOGO! 8 base modules, drag-and-drop virtual network lines between them, and download the resulting network configuration alongside the user program. The tool also differentiates between three classes of lines that appear on the network canvas: blue (configured, selectable), gray (placeholder or auto-created), and green (the physical/logical Ethernet LAN).

Prerequisites

Before creating network connections, gather the following hardware, software, and configuration inputs:

• Two Siemens LOGO! 8 base modules (for example 6ED1052-1MD08-0BA2 with display, or 6ED1052-1HB08-0BA2 pure). Both should run the same firmware generation; mixing 0BA0/0BA1 with 0BA2/0BA3 in a project is supported but limits connections to the older device.
• LOGO!Soft Comfort V8.1 or later installed on the engineering PC. The free LOGO!Soft Comfort Demo version (V8.x) is sufficient for offline configuration but cannot download to hardware without a valid license.
• An Ethernet switch or a direct crossover cable. The LOGO! 8 port auto-negotiates MDI/MDIX, so either a patch cable or a crossover cable works point-to-point.
• Static IP addresses assigned to both modules on the same subnet (default is the 192.168.0.x range used by Siemens factory defaults, but any RFC1918 subnet is valid).
• The LOGO!Soft Comfort project file (.lsc) must contain both base modules as separate devices in a single network project. Insert additional devices via the toolbar icon Add LOGO! Base Module or via the menu File → New → Network Project.

Step-by-Step: Creating a Network Connection Between Two LOGO! 8 Modules

Step 1 - Build the network project

1. Launch LOGO!Soft Comfort and select File → New. From the wizard, choose Network Project rather than the single-device default.
2. Add the first LOGO! base module. The first device added is conventionally labeled Logo_1 by the tool; you can rename it in the device properties.
3. Add the second LOGO! base module. The tool will name it Logo_2.
4. For each device, double-click and set the IP address, subnet mask, and the network identifier (TSAP if used; LOGO! uses fixed TSAPs per firmware generation). The default is to leave the LOGO! assigning the address manually on the unit itself, in which case the tool can read the address via Tools → Detect LOGO! Devices.

Step 2 - Decide whether to draw a link line first

Per the LOGO!Soft Comfort online help (chapter Connecting LOGO!s in a network), a manual drag-and-drop line is not strictly required to create a network connection. The connection can be generated implicitly by dragging a wire from a logic block in Logo_1's FBD diagram to an input/output of Logo_2 (or vice versa). However, drawing the line on the network canvas first has the following practical advantages:

• It documents the network topology visually before logic is added.
• It pre-allocates the local connector on the client (Logo_2) and the source connector on the server (Logo_1), avoiding later renumbering.
• It allows the developer to assign client/server roles in one step without opening the dialog box per I/O symbol.

If you choose to draw the line first, follow the procedure in Step 3. If you skip the manual line and create the connection implicitly through FBD wiring, jump to Step 4.

Step 3 - Drag-and-drop the blue link line

1. On the network canvas, hover the cursor over a connector on Logo_1 (a small dot adjacent to the base module rectangle).
2. Click and hold the left mouse button. A rubber-band line follows the cursor.
3. Drag the line to the desired connector on Logo_2 and release the mouse button.
4. The line turns blue, indicating it is the currently selected connection. At this point the source is Logo_1 (Server) and the target is Logo_2 (Client) by default, because Logo_1 is the one that owns the published I/O.

Step 4 - Configure the connector parameters

1. Click the blue line to select it; the line is highlighted in dark blue.
2. Double-click to open the Network Connection Properties dialog.
3. On the server side, choose whether the published signal is a Digital Input, Digital Output, Analog Input, Analog Output, or a Network Input/Output (NI/NA virtual bit/word).
4. On the client side, choose the destination symbol, e.g. NI1 for a network bit or NAW2 for a 16-bit analog network word. The client uses NI/NA as ordinary FBD inputs.
5. Click Apply. The blue line is now a fully configured network connection.

Step 5 - Auto-create connections from the FBD

1. Open Logo_1's diagram and place a function block, e.g. an AND gate.
2. Click an input pin of the block and drag the wire toward the right edge of the canvas.
3. When the cursor approaches the right edge, a dropdown appears listing all base modules in the project. Select Logo_2 → NI3.
4. Release. A new connection is created and a gray line appears on the network canvas between Logo_1 and Logo_2.
5. Double-click the gray line to assign the server-side source I/O; the line turns blue once parameters are saved.

Interpreting the Line Colors

LOGO!Soft Comfort uses three line colors on the network canvas. Each color is significant and the meaning does not change after the project is downloaded to the hardware:

When the project is downloaded and the physical Ethernet is plugged in, the green LAN line is the only line that is recomputed at runtime. The blue and gray lines describe the logical network connections stored in the LOGO! firmware. After the LOGO! powers up and resolves all configured connections, the LOGO! display shows a dedicated network diagnostics menu (Diagnostics → Network) where successful and failing connections are listed with their connection number and target IP.

Client/Server Role Assignment

LOGO! 8 can act as both a client and a server at the same time. In a network project, the source of a connection is the server and the target of a connection is the client. When you draw a line by dragging from Logo_1 to Logo_2:

• Logo_1 publishes an I/O symbol; Logo_1 is the server.
• Logo_2 receives the symbol through an NI/NA virtual memory address; Logo_2 is the client.

To swap roles, click the existing blue line and select Reverse Direction in the toolbar. After reversal, Logo_1 becomes the client and Logo_2 the server. The same effect is obtained by editing the Source and Target fields in the connection properties dialog.

A single LOGO! 8 can simultaneously serve up to 16 network connections. So Logo_1 may be the server for Logo_2 and the client of Logo_3 without any conflict, as long as no single peer LOGO! exceeds 16 outgoing/incoming connections.

Verifying the Connection

1. Save the project (File → Save As).
2. Select Tools → Ethernet → Connect in LOGO!Soft Comfort. Pick the IP of Logo_1. The PC will establish a connection.
3. Select Tools → Transfer → PC → LOGO! to push the program. Repeat for Logo_2 if the project is split into two separate .lsc files (the tool will offer to push to all devices in a network project at once).
4. On the LOGO! display, press ESC to reach the main menu, then navigate to Diagnostics → Network. Each configured connection is listed with its state: OK, Initializing, or Error.
5. In LOGO!Soft Comfort, switch to Online → Network View. The green LAN line should now show both base modules in the same broadcast domain. Hover the cursor over each blue line to see the live state of the connection.
6. Force a value change on Logo_1's source output (using Online → Simulation with a real LOGO! attached). The corresponding NI/NA on Logo_2 should update within the LOGO! scan cycle, typically within 50-100 ms for digital signals and within one LOGO! cycle (~250 ms default) for analog values.

Connection Counts and Resource Budgets

Each LOGO! 8 base module reserves internal resources for network communication. Use the following budget as a reference when planning a project with more than two modules:

For a two-module project, the practical limit is rarely exceeded; the budget becomes critical only when several LOGO! 8 modules share I/O with one or more S7-1200 controllers or with a SCADA HMI on the same network.

Common Configuration Issues and Corrections

Connection shows "Error" on the LOGO! display

• Verify both base modules are on the same subnet. A 192.168.0.10/24 unit cannot reach a 192.168.1.20/24 unit without a router.
• Check that Ethernet is enabled on the LOGO! (menu Settings → Network). Some firmware versions require enabling the Network Access flag before any connection is allowed.
• Confirm the LOGO!Soft Comfort project assigns the IP that matches the actual unit. A misnamed Logo_1 with IP 192.168.0.10 linked to a hardware LOGO! at 192.168.0.20 will not connect.

Network connection is created but the value is always zero

• Open the connection properties and confirm the Source is set to an actual output or NI/NA symbol that the server LOGO! is driving. A connection from a server input will always read 0 because inputs cannot be published.
• Verify the destination is a writable NI/NA symbol. A network output (NQ/NAQ) is write-protected; trying to feed a server output into a server NQ slot on the same module silently fails.

Green line is missing on the network canvas

• Green lines appear only after the tool has detected the devices on the LAN. Run Tools → Detect LOGO! Devices first.
• If the network is segregated by VLAN, the green lines will not appear and the project must be validated manually.

Connection drops intermittently under load

• Reduce the analog update rate by using a slower block execution (e.g. debounce / on-delay blocks before publishing).
• Check that the network switch does not have a port-security MAC limit lower than the number of MACs on the LAN (LOGO! uses one MAC per port).
• Verify cable length is within 100 m for Cat5e/Cat6 segments.

Best Practices for Multi-LOGO! Projects

1. Adopt a fixed IP addressing scheme (e.g. 192.168.0.10 through 192.168.0.20 for 16 modules) and document the assignment in the project header.
2. Use NI/NA symbols rather than raw inputs/outputs as the published I/O. This decouples the published signal from physical wiring changes.
3. Reserve connection #1 of each LOGO! for diagnostic traffic (status word to a master LOGO! or to a S7-1200).
4. Keep all firmware revisions on a site uniform. Mixing 0BA1 with 0BA3 means every project is restricted to the smaller connection budget.
5. After every firmware update, re-validate the network project, because Siemens occasionally changes connection limits between firmware generations (e.g. 0BA8 FS:05 raised the per-base limit from 8 to 16).

Frequently Asked Questions