Configuring LOGO! 8 Web Server for Remote Temperature Monitoring

Overview

The Siemens LOGO! 8 base module (order family 6ED1052-xxx08-0BA8) ships with an integrated Ethernet web server that is part of the firmware and does not require an additional license. The web server reproduces the on-device display of the LOGO! or of an attached Text Display External (TDE, 6ED1055-4MH08-0BA0) and exposes a subset of the controller's variables, I/O status flags, and programmed message texts to any HTML5-capable browser. Operators can read live process data and write to variables that have been declared as Changeable from a remote PC, smartphone, or tablet without installing vendor plug-ins. Because the web server is bi-directional, it is suitable for applications such as remote temperature monitoring with adjustable setpoints, fan start/stop commands, and acknowledgment of alarm message texts.

Unlike the LOGO! Soft Comfort engineering link (which is a one-to-one programming path), the web server is intended for ongoing operator use. It is not a SCADA package: only programmed message texts and the variables you explicitly publish via the message-text configuration are visible. System menus (clock, language selector, program name, stop/run toggle, SD-card manager, diagnostic buffer) are never reachable from the web view. This article walks through enabling the web server, defining the variables exposed through message texts, configuring the access control list, hardening the network path, and validating the link end-to-end.

Two firmware tiers are relevant when planning the deployment:

• 0BA8 FS:01 – FS:03: HTTP only on TCP 80. Up to 4 ACL entries. No HTTPS, no built-in certificate manager.
• 0BA8 FS:04 (LOGO! 8.3) and later: HTTPS on TCP 443 with a built-in certificate manager, up to 8 ACL entries, optional web-server password. The Siemens product page for LOGO! 8.3 lists FS:04 as the current revision at the time of writing. Confirm the exact FS level on the device with LOGO! > Diagnostics > Firmware or in LOGO! Soft Comfort's Tools > Detect Target dialog.

Prerequisites

• LOGO! 8 base module with Ethernet: 6ED1052-1MD08-0BA8 (LOGO! 8.3, FS:04 or later recommended for HTTPS) or earlier 0BA8 part numbers such as 6ED1052-1CC08-0BA8.
• LOGO! Soft Comfort V8.3 or later engineering software (Siemens article 6ED1058-0BA08-0YA1) loaded with the project that drives the application.
• TDE (Text Display External), part number 6ED1055-4MH08-0BA0, is optional. The web server mirrors either the base-module display or the TDE display, depending on which is selected in the project under File > Properties > Display.
• Ethernet switch or direct patch cable (Cat 5e or higher) for local commissioning.
• IP address plan: assign the LOGO! a static IPv4 address inside the operations subnet. DHCP is allowed but discourages access-list maintenance.
• For remote access across the Internet: a site router with VPN, a Siemens LOGO! CMR 2020 / LOGO! CMR 2040 cellular router, or – strongly discouraged – port-forwarding on a public IP.
• Browser: Chrome 90+, Firefox 90+, Edge 90+, or Safari 14+ on a PC, Android, or iOS device.

LOGO! 8 Web Server Architecture

The web server runs as a service inside the LOGO! 8 firmware and listens on TCP port 80 (HTTP) and, on FS:04 or later, TCP port 443 (HTTPS). It exposes three logical resources:

1. Status page – reflects the current state of the digital inputs (I1–I24), digital outputs (Q1–Q20), analog inputs (AI1–AI8), analog outputs (AQ1–AQ8), and the marker/flag words (M1–M27). Bit-level and word-level variables referenced inside message texts can be toggled or set from this page.
2. Message-text views – a faithful rendering of every message text block programmed in the LOGO! Soft Comfort diagram. Each message-text line can embed up to four variable placeholders, with scaling factors configured in the editor.
3. Control widgets – buttons and number-entry pads rendered next to message texts that drive specific bits or analog words. Only widgets explicitly created in the message-text configuration are exposed.

The TDE's keypad (F1–F4, ESC, OK, cursor arrows) is emulated in the browser, so cursor and OK commands attached to a message text can be triggered remotely. System menus, including the clock, the language selector, the program name, the stop/run toggle, and the card/SD management, are not reachable from the web view.

Web Server vs TDE vs LOGO! App

Step-by-Step Configuration

1. Program the message texts and exposed variables in LOGO! Soft Comfort

Open the project in LOGO! Soft Comfort. For each temperature setpoint that operators must be able to adjust, drop a message-text function block onto the diagram and embed the analog variable placeholder:

1. From the toolbar, choose Special > Message Text and place the block at the rung where the operator's view must be live.
2. Double-click the block to open the editor. The Message Text tab is where the on-screen string is built. Use the Insert Variable button to add the analog setpoint tag (for example, the output of an analog amplifier, the setpoint of a PI controller, or the input of a threshold switch).
3. Switch to the Message Properties tab. The Web access checkbox must be ticked for the variable to be reachable from the browser. The Changeable checkbox enables write-back from the web server. Without these, the web page renders the text but the value is read-only.
4. Set the variable's min/max clamp in the same dialog (e.g. -20 °C to +80 °C) so that an operator typing a number outside the range is rejected.
5. Click OK, save the project, and download it to the LOGO! 8 with the F8 hotkey or Tools > Transfer > PC → LOGO!.

2. Configure the IP address and enable the web server

On the LOGO! base module, navigate with the cursor keys to Network on the integrated display, or use the LOGO! Soft Comfort Tools > Ethernet Connections dialog:

• IP address: assign a static address inside the operations network (e.g. 192.168.10.50/24). Avoid the 192.168.0.0/24 and 192.168.1.0/24 segments if those are used by office equipment.
• Subnet mask: 255.255.255.0 for a /24 network.
• Gateway: the router's LAN address, required if the operator will reach the LOGO! from outside the local subnet.
• Web server: Enabled. On 0BA8 units this setting is exposed through the LOGO! Soft Comfort online menu and on the integrated display under Network > Webserver.
• HTTPS: from FS:04 onward, select Enable HTTPS and load a certificate through Tools > Certificate Manager. Self-signed certificates work for closed systems; production deployments should use a CA-signed cert.

3. Configure the access control list (ACL)

The web server ships with the ACL disabled. The first thing to switch on is a per-IP filter, otherwise the LOGO! responds to every host on the LAN:

1. In LOGO! Soft Comfort, choose Tools > Access Control (or on the device: Network > Access Control).
2. Set Web Server Access to Enable.
3. Add the IP address (or subnet) of every client that should be allowed. Up to 8 entries are supported in firmware FS:04; FS:01–FS:03 supports 4.
4. Tick Apply changes to LOGO! and download.

4. Map the variables that must be writable

The web server only writes back to variables that are explicitly declared as Changeable in the message text. To allow the operator to change a temperature setpoint:

1. Open the message text that contains the setpoint variable (e.g. the analog setpoint of a PI controller, an analog threshold switch, or an analog multiplexer output).
2. Tick Changeable in the Message Properties dialog.
3. Define a minimum and maximum clamp to prevent the operator from typing an out-of-range value (e.g. -20 °C to +80 °C for a refrigeration plant).
4. Re-download the project.

5. Test locally

From a PC on the same subnet, open a browser and enter http://192.168.10.50 (substitute the LOGO!'s IP). The status page should load within 2 seconds. Click any message text with a writable variable and confirm that a number-entry pad appears. Change the value, press OK, and verify on the LOGO!'s physical display that the setpoint was accepted.

Variable Type Reference

Network Access for Remote Operators

Local access covers commissioning. For remote operators, you must put the LOGO! on a routable path:

LOGO! App Alternative

The Siemens LOGO! App (Android, iOS) provides a mobile-friendly front end that speaks the same protocol as the web server. The app is free, requires no per-user license, and adds:

• Auto-discovery of LOGO! 8 modules on the local Wi-Fi network.
• A login screen that prompts for the LOGO!'s IP and the optional web-server password (FS:04 onward).
• Push notifications when a configured alarm message text becomes active.

The app does not extend the set of variables beyond what the web server exposes – it is a client, not a new service. If a setpoint is not marked Changeable in LOGO! Soft Comfort, it is not adjustable from the app either. The "Connection in Progress" symptom that operators often report usually maps to one of three causes: the app is pointed at the wrong IP, the phone's address is not on the ACL, or the phone and the LOGO! are on different subnets that cannot route to each other.

Scan-Time and Performance Impact

The embedded web server shares the LOGO!'s 16-bit CPU with the user program. Each connected browser triggers a polled refresh at roughly 1 Hz, which adds a small overhead per cycle:

If the application relies on a fast PI control loop (sub-50 ms cycle), keep the number of web users to four or fewer. The LOGO! 8 does not throw an explicit error code when overloaded; instead, the web page stalls and eventually times out. Watch the diagnostic buffer in LOGO! Soft Comfort (Tools > Online > Diagnostic Buffer) for Web server queue overflow entries when this happens.

Verification Checklist

1. Open the web server in a browser from an allowed IP and from a blocked IP. Allowed IP returns HTTP 200 OK; blocked IP returns HTTP 403.
2. Toggle a digital flag mapped to a writable bit. The physical output must follow within 200 ms – this confirms the web server write path is alive.
3. Change a temperature setpoint from the web page and verify the value on the LOGO!'s integrated display. The reading must match the new value.
4. Power-cycle the LOGO! and re-confirm that the web server comes back online within 10 seconds and that the ACL is still in effect.
5. Test HTTPS if enabled: navigate to https://192.168.10.50 and confirm the certificate is valid.
6. From a remote client behind the site VPN, repeat steps 1–3 to validate the routed path.

Troubleshooting Matrix

Security Notes

• Change the default LOGO! password (if set) before exposing the device beyond the commissioning bench.
• Restrict the ACL to operator subnets only; never put a 0.0.0.0/0 entry in the list.
• On FS:04 or later, use HTTPS only; redirect HTTP requests to HTTPS in the network configuration.
• Patch the LOGO! firmware when Siemens issues a security note. The Siemens Industry Online Support portal lists advisories that affect LOGO! 8.
• Document the ACL, the certificate fingerprint, and the remote-access path in the project's Functional Safety / Cybersecurity file so the controls survive a maintenance handover.

FAQ