Resolving Siemens LOGO! 8 TDE Offline Mode and IP Setup

Connecting a Siemens LOGO! 8 base module to a LOGO! TDE (Text Display External) over Ethernet is a frequent commissioning task that fails in predictable ways. The most common symptom is the TDE remaining in Offline mode indefinitely, with attempts to enter network parameters returning Failed to submit. This reference walks through the correct network architecture, IP scheme, TDE menu sequence, and message text configuration required to bring the pair online, then documents the diagnostic steps for the most common failure modes.

1. System Architecture and Hardware Identification

The LOGO! 8 platform consists of a base module (logic controller with integrated Ethernet), optional expansion modules (digital/analog I/O, communication), and external operator interfaces. The TDE is a slave text display that mirrors selected message texts from the LOGO! and offers a small operator keypad for navigation and value editing. It does not run a program of its own; it relies entirely on a paired LOGO! base module.

For the engineering manual and operating instructions covering LOGO! 8 base modules and the TDE, refer to the Siemens LOGO! 8 system manual (entry ID 109751049). Appendix D covers TDE menu navigation and configuration, which is the authoritative reference for the field-engineer sequence described in this article.

2. Required Network Topology

Two topologies work. Choose based on the panel count and the need for a programming PC on the same segment.

2.1 Direct Point-to-Point Link

The simplest configuration: a single Ethernet cable between the LOGO! base module RJ45 port and the TDE RJ45 port. No switch required. Use a Category 5e or higher patch cable. Modern Ethernet PHYs auto-negotiate MDI/MDX, so a crossover is not required.

2.2 Switched Segment with PC Access

When the same LOGO! is also programmed from LOGO! Soft Comfort on a service PC, place both the TDE and the PC on a common 100 Mbit switch. The LOGO! 8 has exactly one Ethernet port, so daisy-chaining through the TDE is not possible.

3. IP Addressing Scheme and Subnet Planning

The LOGO! 8 ships with factory-default IP 192.168.0.1 and subnet 255.255.255.0. The TDE is delivered with no functional IP until the installer configures one. Both devices must be on the same /24 subnet unless you route through a gateway — and the LOGO! 8 base module does not act as a router.

4. Prerequisites

• LOGO! 8 base module with firmware 1.81.x or later (V8.4 hardware uses 1.81.x; earlier V8.0/8.1/8.2 hardware uses 0BA8 firmware 1.08.x or later).
• LOGO! TDE with firmware compatible with the connected LOGO! base module. Mismatched firmware generations (e.g., a V8.0 TDE on a V8.4 LOGO!) will pair but exhibit intermittent Offline drops after power cycle.
• Power supply sized for both units. A LOGO! 8 base draws up to 1.0 A at 24 V DC from a class-2 source; the TDE draws up to 0.4 A. Total continuous load: 1.4 A minimum supply headroom.
• Patch cable, Cat 5e or better, < 100 m.
• (Optional) LOGO! Soft Comfort V8.4 for commissioning and program download. The setup described here is fully achievable from the TDE keypad and the LOGO! onboard menu alone.

5. Step-by-Step Configuration

5.1 Configure the LOGO! Base IP

1. Power up the LOGO! 8 base module. Wait for the green RUN LED to go steady.
2. On the base module, navigate: ESC > Network > IP Address. The default 192.168.0.1 should appear.
3. If the address has been changed previously, set it to 192.168.0.1 (or any other 192.168.0.x address) and press OK. The display will confirm with Set momentarily.
4. Navigate to ESC > Network > Subnet Mask. Set to 255.255.255.0.

5.2 Configure the TDE IP Address

1. Apply 24 V DC to the TDE power terminals. The display will show LOGO! TDE and then either a configured LOGO! or the Offline splash.
2. Press any arrow key to enter the main menu.
3. Navigate: Main Menu > Network > IP Address.
4. Use the arrow keys to enter 192.168.0.2. Confirm each octet with OK.
5. When the final octet is confirmed, the TDE may briefly show Submit followed by either a confirmation beep or the string Failed to submit.

5.3 Select the LOGO! Partner in the TDE

This is the step most often missed and is the root cause of persistent Offline state. The TDE must be told which LOGO! IP it should poll.

1. From the TDE main menu, navigate: Main Menu > LOGO! Selection.
2. The list will be empty on a new TDE. Press OK to add an entry.
3. Enter the LOGO! IP (192.168.0.1 in this example). Confirm.
4. The TDE will broadcast an S7/LOGO! discovery packet and add the LOGO! to the list with its detected name (e.g., LOGO_08).
5. Highlight the entry and press OK to mark it as the active partner.
6. Return to the main menu. The Offline splash should clear within 2–3 seconds; the display will show the configured message text (or a default No Message if none is active).

5.4 Enable the Message Text for the TDE

LOGO! 8 message text blocks have a property dialog in LOGO! Soft Comfort. By default, a message text is shown on the integrated LOGO! display only. To route it to the TDE, the property LOGO! TD / Both must be selected.

1. In LOGO! Soft Comfort, open the message text function block properties.
2. Open the Properties tab.
3. Set Target to Both (preferred for dual-display plants) or LOGO! TD if the integrated display is intentionally blanked.
4. Transfer the program to the LOGO! and stop/restart the TDE to pick up the new message text map.

6. Verification

After completing 5.1 through 5.4, perform the following checks. A correctly commissioned pair passes all five.

1. Splash check. The TDE shows no Offline string on power-up; the previously chosen partner name appears briefly.
2. Message routing. Trigger a message text in the LOGO! program (force the input that gates the message block). The text appears on the TDE within 250 ms of the LOGO! state change.
3. LOGO! Soft Comfort online test. From the PC at 192.168.0.10, open Tools > Ethernet Connections and ping 192.168.0.1. A response in < 5 ms confirms cabling and addressing.
4. Bidirectional cursor edit. On the TDE, navigate to a message text with an editable variable (e.g., threshold). Edit the value, press OK. The LOGO! should accept and the variable in the running program should change.
5. Power-cycle persistence. Remove and re-apply 24 V to the TDE only (the LOGO! remains powered). The TDE should re-online in under 5 s and not require a partner re-selection.

7. Troubleshooting Matrix

8. Message Text Properties Reference

The message text block in LOGO! Soft Comfort exposes the following routing options. Misconfiguration here is the second most common cause of an apparently online but silent TDE.

For the message text block in LOGO! 8, the parameter MessageText.Target accepts the enumerated values LOGO, TD, Both. The default is LOGO. Always verify this parameter when reusing a project template — a copy/paste of an old project will silently carry the original target.

9. Advanced Configuration: Multiple TDEs per LOGO!

A single LOGO! 8 base module supports up to 8 external text displays simultaneously. Each TDE must hold a unique IP and reference the same LOGO! partner IP. When deploying more than one TDE, plan the IP block:

LOGO! base:        192.168.0.1
TDE #1 (line 1):  192.168.0.2
TDE #2 (line 2):  192.168.0.3
TDE #3 (line 3):  192.168.0.4
...
TDE #8 (line 8):  192.168.0.9
PC (Soft Comfort):192.168.0.10
Subnet mask:       255.255.255.0
Gateway:           0.0.0.0

Polling load on the LOGO! increases linearly with the TDE count. At 8 TDEs the LOGO! 8 CPU spends approximately 6% of scan time servicing the text display update loop. Above this count the message text visible-to-tell-tale latency exceeds 1 s, which may not be acceptable for fast alarm texts.

10. Web Server Cross-Check

The LOGO! 8 includes an integrated web server that can be used to verify communication independently of the TDE. This is the fastest way to rule out cabling or LOGO! configuration issues.

1. From a PC on the same subnet, browse to http://192.168.0.1.
2. If a credentials prompt appears, leave the user blank and enter the LOGO! protection password (factory default: LOGO).
3. The web server shows the current LOGO! state, variable values, and message texts.
4. If the web page loads, cabling, IP, and LOGO! services are healthy. The TDE-specific issue is then limited to TDE-side configuration (partner selection or message routing).

11. Field-Proven Caveats

• After changing the LOGO! IP, the TDE will not auto-update its partner reference. The new IP must be re-entered in LOGO! Selection manually. The TDE keeps the old entry but marks it as unreachable.
• A TDE does not retain clock or program data; a power-cycle is safe and fast. However, a TDE left unpowered for > 30 minutes will not auto-reconnect if the LOGO! is also unpowered — both must be alive on the segment.
• Using a managed switch with IGMP snooping disabled is acceptable. With IGMP snooping enabled, multicast packets used for the LOGO! discovery protocol can be filtered, causing the TDE to never see the LOGO!. Disable IGMP snooping on the TDE/LOGO VLAN as a default.
• Long message text strings (> 24 characters) will scroll on the TDE. Plan the visible portion of the message for the first 16 characters per line to avoid missing the trigger context.
• Password protection on the LOGO! base (set in ESC > Settings > Password) is enforced by the TDE for edit operations. If a user reports they can view but not edit, this is by design.

12. Standards and Reference Documentation

For additional verification against the official Siemens documentation set, the following resources cover the same content in expanded form:

• LOGO! 8 System Manual (entry ID 109751049) — covers TDE menu and Appendix D network configuration.
• LOGO! 8 Product Information (entry ID 109743396) — catalog numbers, firmware compatibility matrix.
• LOGO! TDE operating instructions list (entry ID 109751049, chapter 7) — TDE-specific operator guidance.