Resolving LOGO! 8.3 Network Connection Failure in LOGO!Soft

Problem Summary

Two Siemens LOGO! 8.3 base modules (order number 6ED1052-2MD08-0BA1) wired into a single Ethernet segment refuse to exchange network inputs (NI) and network outputs (NQ) even though the LOGO!Soft Comfort (LSC) project compiles cleanly, runs in simulation without errors, and both base modules can be placed online individually for monitoring and force operations. The physical link is good, the IP addresses are on the same subnet, and the same FBD program has been uploaded to each unit. Network I/O remains at zero in both directions until a single checkbox in the LSC project tree is enabled. The defect is not in the wiring, the firmware, or the program logic. It is a configuration omission in the device pairing step that is easy to miss because the simulation engine does not validate it.

Affected Hardware and Firmware

The order number 6ED1052-2MD08-0BA1 decodes as follows:

• 6ED1052 — LOGO! 8 base module family
• 2 — integrated 6-line LCD with cursor keys
• MD08 — 24CEo variant: 24 V DC supply, 8 digital inputs (4 of which are also usable as analog 0–10 V inputs), 4 solid-state digital outputs, 1 Ethernet RJ45 port
• 0BA1 — order suffix mapped to LOGO! 8.3 (also called 8.FS04), firmware 1.0.x.x

Cross-references for the LOGO! 8.3 generation as published by Siemens are documented in the LOGO! 8 system manual (Siemens Support entry ID 109751612) and the Siemens LOGO! product page. Generation compatibility for a single project network is summarised below.

Root Cause

When the second LOGO! is added as a network partner inside the LSC project tree, the developer is presented with a list of available device generations. The list, in LSC V8.3, reads:

• LOGO! 0BA7
• LOGO! 0BA8 standard
• LOGO! 8.FS4
• LOGO! 8.1 & 8.2
• LOGO! 8.3

Selecting "LOGO! 8.3" inserts a device that matches the 0BA1 order suffix and firmware 1.0.x.x. The Add Device wizard then offers a second pane in which the S7 communication protocol must be enabled by ticking the S7 tab / S7 column for the partner. If that check is left off, LSC generates a project that contains a network partner entry but no S7 client/server binding. The project still compiles and the simulation engine still exchanges NI/NQ values, because the simulator does not perform the S7 handshake that the real firmware performs on every scan. The result is a project that simulates cleanly and fails on hardware.

This is the precise symptom reported in the source incident: "the program is solid … I can take both online individually and activate inputs and outputs but the network inputs and outputs will not work. It works fine in simulation mode." The poster's eventual fix was to scroll the device wizard to the second page and tick the S7 tab for both LOGO! nodes. The fix took effect immediately after download to both BMs.

Why the Simulation Mask the Defect

The LSC simulation kernel runs the FBD program on the PC's CPU and emulates the network block in shared memory. The on-board firmware, by contrast, only exchanges NI/NQ bytes when a valid S7 connection is established between the master and the partner. The S7 connection has two halves:

1. An S7 server block embedded in the master BM, which advertises its NI and NQ points on TCP port 102 (the standard S7 port).
2. An S7 client block embedded in every other BM in the project, which opens a TCP connection to the server's IP address and reads/writes the NI/NQ bytes.

If the S7 tab is unchecked when the partner is added, LSC does not generate either block. The simulation therefore has no S7 stack to instantiate and silently substitutes a stub. The on-board firmware has no stub and simply returns zeros for every NI/NQ read, which is exactly what the source poster observed.

Prerequisites

1. LOGO!Soft Comfort V8.3 or later installed on a Windows 10 / 11 PC. Earlier V8.x releases expose LOGO! 8.1/8.2 but not the 8.3 profile, so a partner insertion will fail or default to a lower firmware image.
2. Both base modules must run LOGO! 8.3 firmware. The version string is visible on the front panel under Menu > Diagnostics > Firmware.
3. An Ethernet switch and CAT5e (or higher) cabling, or a direct patch cable for a two-node network. Auto-MDIX on the BM's RJ45 jack supports both crossed and straight cables.
4. Each BM assigned a unique IPv4 address on the same subnet. The default static address is 192.168.0.10 with mask 255.255.255.0. DHCP is supported but discouraged in production.
5. One BM designated as the S7 server (the master) and the other as the S7 client. In practice both BMs can act as server because every BM publishes its own NI/NQ; LSC still requires that one role be assigned in the network table for the binding to compile.

Step-by-Step Solution

Step 1 — Verify the Firmware of Both BMs

On the BM with display, navigate to Menu > Diagnostics > Firmware. The version line must read V1.0.x.x. On a BM without a display, connect over Ethernet from LSC using Tools > Transfer > Ethernet Connections; the firmware version appears in the connection dialog. If a node shows V0.x (i.e., 8.0, 8.1, 8.2), you can still include it in the network, but the LSC project must be authored at the lowest firmware level in the network to keep generation compatibility.

Step 2 — Open the Project in LOGO!Soft Comfort V8.3+

Launch LSC and open the project (.lsc or .lscx) that contains both LOGO! programs. If the project was originally created in V8.0 or V8.1, LSC offers to convert it on open. Accept the conversion and re-save under a new filename so the original V8.0 binary is preserved as a fallback.

Step 3 — Add the Partner LOGO! with the S7 Tab Enabled

In the project tree on the left, right-click the parent project node and choose Add Device > LOGO! 8.3. The Add Device wizard shows the available generations. After selecting "LOGO! 8.3," advance to the configuration pane and tick the S7 column / S7 tab. Repeat for each partner. The S7 column is the same column that the source poster failed to enable.

Step 4 — Configure NI / NQ Mapping

On the master BM's FBD, drag the network inputs (NI1..NI64) onto the inputs of the FBD blocks. On each partner BM, drag network outputs (NQ1..NQ64) from the function block outputs and assign them to NI on the master side. The LOGO! 8.3 firmware supports 64 NI and 64 NQ per BM, organised as 8-byte vectors in the project. The mapping is set in Project > Network Properties.

Step 5 — Compile and Download

Press F5 or click the Download toolbar icon. LSC prompts for the target BM (IP address). Download to the master first, then to the partner. The master must always be downloaded last when the project contains a server role change.

Step 6 — Save the Corrected Project

Use File > Save As to commit the corrected .lsc / .lscx file. If the project will be deployed to a fleet, export to a micro-SD card image using Tools > Export to SD Card. The SD card can be hot-inserted into any LOGO! 8.3 BM to install the program without a PC.

Verification

1. Place both BMs online in LSC using Tools > Online > Connect. The status bar should read "Connected" for both.
2. Force a local input high on the master. The corresponding NQ on the partner should toggle high in the online view within one scan cycle of the master (typically 50–100 ms with the default 10 ms cycle).
3. Reverse the test: force an input on the partner, confirm the master's NI updates.
4. Ping the partner's IP from the PC. A successful reply confirms the IP layer; a successful NI/NQ exchange confirms the S7 layer.
5. Open the LOGO! onboard web server at http://192.168.0.10 (or the assigned address) and inspect the Network I/O page for live NI/NQ state.

Configuration Parameter Table

Network Architecture and Limits

• Up to 16 LOGO! 8 nodes can be added to a single project network. The network is logically peer-to-peer, but LSC requires that one node be assigned the S7 server role for the NI/NQ binding to compile.
• Each BM publishes 64 NI and 64 NQ in firmware 1.0.x.x. Earlier 0BA8 firmware exposes a smaller vector (typically 8 NI / 8 NQ). When mixing generations, the NI/NQ count must be set to the lowest common denominator.
• The Ethernet interface is 10/100 Mbit/s, auto-negotiating, full duplex. Standard Cat5e cabling applies.
• Default static IP is 192.168.0.10 for slot 0, 192.168.0.11 for slot 1, 192.168.0.12 for slot 2, 192.168.0.13 for slot 3.
• The subnet mask default is 255.255.255.0. The gateway is left blank unless the LOGO! must reach a cloud service such as the LOGO! Access Server.
• LOGO! 8.3 does not support NAT, VPN, TLS, NTP, or SNMP. Remote access requires a LOGO! CMR2020 (4G cellular router, order code 6BK1700-0HA00-0AA0) or a separate S7-1200 acting as a gateway.

Common Errors and Their Solutions

Diagnostic Indicators and Display Messages

The RJ45 jack has a green link LED and a yellow activity LED. The integrated display (on the 2xx variants) shows a small Ethernet icon in the status bar; the icon turns red and shows an exclamation mark when the S7 client cannot reach its server. The full diagnostic string is reachable from Menu > Network > Network Status. Common messages include:

• No partner — partner IP not reachable; check cabling and IP table.
• S7 error — S7 tab not enabled in LSC, or partner firmware mismatch.
• OK — S7 handshake completed; NI/NQ should be live.

Tools > Ethernet Connections Dialog

The Tools > Ethernet Connections dialog in LSC controls which IP slot the PC will use to reach a target BM. Slot 0 maps to 192.168.0.10, slot 1 to 192.168.0.11, slot 2 to 192.168.0.12, slot 3 to 192.168.0.13. Populate all four slots before deploying to a fleet. The dialog also stores the last-seen MAC address of each BM, which is useful for distinguishing two identical units on a test bench.

Migration from LOGO! 0BA7

LOGO! 0BA7 supports a simpler master-slave network that does not use the S7 protocol. If a 0BA7 must be replaced with a 0BA1 in an existing project, the LSC migration tool rewrites the network block to the S7 syntax automatically. The developer must still enable the S7 tab in the project tree, which is the same operation described in Step 3 of the procedure above. After migration, verify NI/NQ mapping against the original project's I/O list.

Cloud and Remote Access

For remote access to a LOGO! 8.3 network, pair the BMs with a LOGO! CMR2020 (order code 6BK1700-0HA00-0AA0) cellular router and use the LOGO! Access Server hosted by Siemens. The CMR establishes a VPN tunnel to the Siemens cloud; the BMs do not need to be reachable from the public Internet. The BM's onboard web server is exposed through the VPN as a normal HTTPS page. Configuration of the CMR is documented in the LOGO! 8 system manual and the LOGO! product page.

Firmware Update Path

LOGO! 8.3 firmware is updated from Tools > Update Firmware in LSC V8.3+. The new firmware file is delivered as a .bin or .upd from the Siemens Industry Online Support portal. A firmware update wipes the user program; reload the project afterwards. Downgrade to a prior 8.x branch is possible but requires re-flashing the previous firmware image through the same menu. Do not downgrade below 0BA7 if the project contains a network block, because the network block will not re-compile.

Related Components

Safety Considerations

Web Server Diagnostics

The onboard web server, available from firmware 8.0 onward, can be reached on port 80 of the BM's IP address. The Network I/O page shows the live NI/NQ vectors in a 64-bit table. Use this page to confirm that the S7 handshake has completed and to differentiate "no data because of a S7 mis-configuration" from "no data because the source signal is actually low." The web server can be password-protected from Project > Web Server in LSC; the default user is admin with no password.

Best Practices for Multi-BM Panels

1. Assign fixed static IPs from 192.168.0.10 upward; reserve the entire 192.168.0.10 – 192.168.0.253 range for the LOGO! fleet to keep DHCP and PROFINET in separate subnets if you add an S7-1200 later.
2. Document the S7 master / client role per BM in the project header comment; LSC does not display the role in the runtime view.
3. Use a managed Ethernet switch with port-level IGMP snooping disabled; the LOGO! S7 link is unicast and IGMP is irrelevant, but a misconfigured switch can drop the TCP keep-alive.
4. Always download the master last. The master holds the S7 server block; a partner BM that comes online before the master will hold its NI/NQ at zero until the master's server block is reachable.
5. Test with two BMs on a bench before adding a third. Each new BM adds a S7 client and increases the master scan time slightly.

Final Diagnostic Checklist

1. Both BMs report firmware 1.0.x.x on the display or in LSC.
2. LSC project tree shows both BMs with the S7 column ticked.
3. Ethernet link LEDs are green on both BMs.
4. Ping from the PC to both BM IPs succeeds.
5. Online view in LSC shows NI/NQ updating within one scan cycle of the partner's input change.
6. Web server Network I/O page shows the same NI/NQ state as the LSC online view.

If any of the above fails after the S7 tab has been enabled, the issue lies in the physical layer, the IP table, or a third BM that was overlooked during the Add Device step. The S7 tab is the most common cause, and the source poster confirmed that enabling it resolved the failure on two 6ED1052-2MD08-0BA1 units in the field.