Troubleshooting Siemens LOGO! 8.4 Email Trigger Failures

1. Problem Description

The Siemens LOGO! 8.4 logic module (part of the LOGO! 8 generation of micro-PLCs) supports outbound email notifications through its integrated Ethernet interface. The notification path is split into two independent subsystems:

• SMTP client — handles transport, authentication, TLS negotiation, and message construction. Configured in the device WebConfigurator under Network → Email.
• Trigger dispatcher — decides when a message is sent. Triggered either by program-side logic (digital inputs, function block outputs, flag bits) or by internal system events (RUN/STOP transitions, power-up, power-down).

The defect described in the field appears when the SMTP client passes its own self-test (the "Send test mail" button in WebConfigurator returns success) but the trigger dispatcher never produces a real message. Program-triggered emails are silently dropped, and the configurable system triggers (start/stop, run/stop) likewise do not produce traffic at the SMTP server.

Symptom summary engineers should look for:

• WebConfigurator → Email → Send test mail returns OK and the message arrives.
• Live tag or boolean transition wired to the email block never results in an outbound message.
• Wiring the trigger to a system event such as RUN → STOP produces no log entry and no server-side delivery attempt.
• No SMTP connection attempts visible in the firewall or in tail -f on the mail server when the program-side trigger fires.

2. Affected Hardware and Firmware

The defect was confirmed on the following LOGO! 8.4 base modules running firmware earlier than V1.84.03:

The matching programming environment must be LOGO! Soft Comfort V8.4 with Service Pack 1 (SP1). Earlier builds of Soft Comfort V8.4 do not always write the updated project metadata expected by the corrected firmware and can re-introduce the issue when the project is re-downloaded.

3. Root Cause Analysis

The trigger dispatcher in the affected firmware revisions contains a state-machine error in the way it links a rising-edge on a configured trigger source to the SMTP transmit queue. The defect is reproduced as follows:

1. The dispatcher initialises correctly on power-up and registers the SMTP client as a valid sink.
2. When a manual test email is invoked from WebConfigurator, the dispatcher is bypassed — the SMTP client transmits directly.
3. When a configured trigger (program tag or system event) fires, the dispatcher queues the request, but the internal handle to the SMTP transmit function is invalid. The entry is dropped without error and without log.

Because no log line is written, the failure is invisible inside the device. A Wireshark capture on the Ethernet segment shows SMTP EHLO traffic only for test mails, never for triggered mails. Server-side, the only sign of life is the test message.

Siemens corrected the dispatcher state machine and the way Soft Comfort V8.4 SP1 serialises the trigger configuration block on download. Both updates are required: the firmware fixes the on-device bug, and the SP1 prevents the configuration that triggers it from being re-written by older project files.

4. Required Updates

Both files are distributed together in the LOGO! 8.4 service pack. Refer to the LOGO! 8.4 system manual (Siemens ID 109751616) and the LOGO! product information page (Siemens ID 109766999) for the canonical firmware download path. Confirm the ZIP signature against the Siemens certificate before deploying to production hardware.

5. Step-by-Step Firmware Upgrade Procedure

5.1 Prerequisites

• PC with LOGO! Soft Comfort V8.4 SP1 installed.
• Ethernet connection from the PC directly to the LOGO! 8.4 base module (point-to-point or via the same switch). No cross-network or routed path.
• 24 V DC (or AC, depending on variant) supply stable; the module must not lose power during the upgrade.
• Project backup (.lsc) of the current logic. The upgrade does not erase user program, but a backup is mandatory.

5.2 Upgrade the Base Module Firmware

1. Open LOGO! Soft Comfort V8.4 SP1 → Tools → Firmware Update.
2. Select Target device → LOGO! 8.4 base module.
3. Browse to the firmware file (typically LOGO_8.4_BM_V1.84.03.upd or similar).
4. Confirm the IP address of the target matches the device under Options → Ethernet Connections.
5. Click Update. The transfer takes 2–6 minutes. Do not interrupt.
6. Wait for automatic reboot. The RUN/STOP LED will cycle.
7. Re-open WebConfigurator and verify Information → Firmware version reports V1.84.03.

5.3 Re-download the Project

1. Open the existing .lsc project in Soft Comfort V8.4 SP1.
2. Compile (F7) to ensure the new project metadata is written.
3. Connect (F8) → PC → LOGO! 8.4.
4. Transfer PC → LOGO! (download program to device).
5. Switch the device to RUN and confirm the program behaves as before the upgrade.

6. SMTP Configuration Reference

All SMTP parameters live in the device WebConfigurator under Network → Email. The values shown below are the ones the engineer should confirm before chasing trigger faults.

Press Send test mail after every credential change. A working test mail is the only reliable way to verify the SMTP client side. If the test mail fails, fix that first; the trigger dispatcher cannot succeed where the test mail fails.

7. Program-Side Email Trigger Programming

LOGO! 8.4 emails are dispatched when the input of the email function transitions from 0 to 1 (rising edge). The function is added to the program from the toolbar: Special → Email, or in circuit-diagram form under SF → E-Mail.

Minimum wiring:

    +-------+        +----------+
 I1 --| AND   |---EN--| E-Mail   |---(send)
 M3 --|       |        | Function |
    +-------+        +----------+

Where:

• I1 is the digital input wired to the alarm condition.
• M3 is a flag bit you use to inhibit sends during commissioning.
• The EN input must pulse (0 → 1 → 0) — a sustained high will fire only on the first edge, not continuously.

To re-arm the email function for repeated alarms, latch the trigger with a pulse generator:

    +-------+        +---------+        +----------+
 I1 --| AND   |---EN--| Pulse   |---IN---| E-Mail   |---(send)
 M3 --|       |        | (1s)    |        | Function |
    +-------+        +---------+        +----------+

The pulse generator output delivers a clean 1-second trigger that the firmware can latch, even if the firmware revision is one of the affected builds — a useful commissioning workaround before the upgrade is in place.

8. System-Event Email Triggers

System triggers are configured in WebConfigurator under Email → Triggers. The available events on LOGO! 8.4 are:

Each event is configured with a subject and a body template. Tag substitution (e.g. %I1 for the state of input 1) is supported in both fields. With firmware earlier than V1.84.03, none of these events produce a transmission even when enabled — a tell-tale sign that the dispatcher is the failure point, not the SMTP path.

9. Verification Procedure

After applying the firmware and Soft Comfort updates, perform the following end-to-end test. Each step must pass before moving to the next.

1. Firmware verification — WebConfigurator → Information: firmware reports V1.84.03 (or later 1.84.x).
2. SMTP verification — Send test mail returns OK and the message arrives.
3. Program trigger verification — force input I1 high, observe that the E-Mail function logs a send attempt in the device diagnostic buffer (Diagnostics → Buffer), and that the SMTP server receives a connection.
4. System trigger verification — toggle RUN/STOP on the device; expect one email on each transition.
5. Body content verification — open the received email and confirm that the tag substitution rendered correctly (e.g. %I1 shows the live state).
6. Negative verification — short the trigger signal to ground, confirm no further mails are sent within 60 seconds (debounce check).

A Wireshark capture filtering on tcp.port == 587 (or your chosen port) during the test is the most authoritative verification — it proves the firmware actually opened the SMTP session, not just that the dispatcher tried.

10. Troubleshooting Matrix

11. Best Practices

• Always apply firmware and Soft Comfort together. The dispatcher fix and the project serialisation fix are a pair — applying only one re-introduces the symptom on the next download.
• Use a dedicated mailbox for LOGO! notifications. Avoid personal accounts; lock the account to an app password with SMTP-only scope.
• Set DNS in WebConfigurator to a server on the local subnet. A public DNS path is one more failure mode you do not need.
• Debounce triggers with a pulse generator rather than wiring raw inputs. This prevents mail storms on noisy signals.
• Log every send to the diagnostic buffer by setting Diagnostics → Log events → Email to On. You will need it during commissioning.
• Document the firmware version in the project header. If you ever swap the base module, you can restore the exact matched firmware/Soft Comfort pair.

12. Frequently Asked Questions