Resolving LOGO! Soft V8 Connection Failures to 6ED1052-1HB00-0BHA

1. Overview

The Siemens LOGO! 8 base module with the part number 6ED1052-1HB00-0BHA4 is a 12/24 V RCE logic module (relay outputs, integrated display, RCE suffix) typically used on UV insolators, ventilation cabinets, small pump stations, and similar skid equipment. The "RC" designation indicates relay outputs, and the "E" indicates integrated Ethernet. Field reports and the question this article was written against describe a unit that, despite the E suffix, is being commissioned against a LOGO! Soft Comfort V8.2.1 workstation through the LOGO! PC cable (the front-panel/PC serial cable, MLFB 6ED1057-1AA01-0BA0 for USB or 6ED1057-1AA00-0BA0 for legacy RS232). The cable enumerates as a virtual COM port — in the case described, COM3 — and LOGO! Soft reports a generic "unknown IP address" or "target not found" error when the user clicks Transfer > PC <-> LOGO!.

The root cause is almost never the IP stack: it is the missing Transfer Mode on the base module. LOGO! Soft, by default, opens the connection dialog assuming Ethernet. Until the user manually selects LOGO! Cable and points it at COM3, the software never instantiates the serial protocol that the front-panel cable expects. This article walks the engineer through the exact key sequences on the LOGO! keypad, the correct selection tree in LOGO! Soft V8.2.1, and the verification steps that confirm a successful program read/write.

2. Problem Definition

The fault surfaces in three reproducible ways inside LOGO! Soft Comfort V8.2.1:

1. The PC <-> LOGO! dialog opens on the Ethernet tab. The user is prompted for an IP address. The base module's actual address (default 192.168.0.5 for an unconfigured RCE module) is unknown to the user, so the software returns "No LOGO! found on the network".
2. The user attempts to enter a serial port number while still on the Ethernet tab — the COM field is greyed out.
3. Even after selecting the LOGO! Cable radio button, the software still reports "Target does not respond" because the base module is in Run mode, not in the PC <-> LOGO! handshake state.

The error text varies by firmware revision of the base module. The V8.2.1-era modules commonly report one of the following messages (raw text from the LOGO! Soft dialog):

3. Root Cause Analysis

The 6ED1052-1HB00-0BHA4 is a LOGO! 8 / LOGO! 8.1 generation base module. Its front-panel RJ45-style programming port uses a Siemens-proprietary serial protocol at 19 200 baud (default) over the LOGO! PC cable. Unlike an Ethernet session, the serial protocol is a master/slave handshake: the PC requests control, the LOGO! must already be waiting in the PC <-> LOGO! menu before any handshake occurs.

Three things must be true for the connection to succeed:

1. The base module is in Transfer Mode — its display shows the icon PC <-> LOGO! and the cursor is blinking on Stop (Run) or Yes (PC Stop) depending on firmware.
2. The correct transport is selected in LOGO! Soft — the LOGO! Cable radio button, not the Ethernet tab.
3. The COM port number matches the cable's enumerated port — verify in Windows Device Manager under Ports (COM & LPT).

Failure of any one of these three produces the symptom. The original field report showed all three conditions violated: the LOGO! was in Run, the user stayed on the Ethernet tab, and the COM field was unaddressed.

4. Prerequisites

Reference documentation:

• Siemens LOGO! product portal (Siemens AG, 2024).
• LOGO! 8 System Manual (entry ID 109757519) — SIOS, 2022.
• LOGO! 8.3 System Manual (entry ID 109759101) — SIOS, 2023.
• LOGO! Soft Comfort V8.2 Operating Manual (entry ID 109751598) — SIOS, 2021.

5. Hardware and Cable Identification

Confirm the part on the device label. The MLFB (Siemens order number) 6ED1052-1HB00-0BHA4 decodes as follows, with reference to the LOGO! 8 catalog structure published in the Siemens Industry Mall:

The 6ED1052-1xx range replaces the older 6ED1052-1MDxx (24 CEo) and 6ED1052-1FBxx (230 RCE) variants. The E suffix denotes the embedded Ethernet port; in many field deployments, that port is left unused because the existing cabinet already integrates a 24 V SELV barrier on the front-panel cable, and the operator is more comfortable with the physical cable approach.

6. Procedure: Enabling Transfer Mode on the LOGO! Front Panel

The 6ED1052-1HB00-0BHA4 has six keys on its integrated display: ←, ↑, ↓, →, ESC, and OK. Transfer Mode is reached through the main menu tree, not through the program editor. Use the key sequence below; the LCD confirms each step.

1. From the default time/date screen, press ← to enter the main menu. The first item is Program (if a program is loaded) or Set... (if no program is loaded).
2. Press ↓ repeatedly until PC <-> LOGO! appears. On a 6-line LOGO! display this is item 4 of 6 in the main menu.
3. Press OK. The display now shows PC <-> LOGO! with a blinking cursor.
4. Press ↓ once. The display shows PC STOP on the first line and No / Yes on the second line.
5. Press → to highlight Yes.
6. Press OK. The display now shows LOGO! <-> PC in the upper line and Stop run pgm in the lower line. This is Transfer Mode — the base module is now waiting for a serial handshake.

The display backlight will pulse slowly to confirm that the module is in PC-link state. The module's relay outputs are forced to OFF (safe state) while Transfer Mode is active. The menu tree is summarised in the diagram below.

Figure 1 — Transfer Mode entry on the LOGO! 6ED1052-1HB00-0BHA4 front panel.

7. Procedure: Configuring LOGO! Soft V8.2.1

1. Launch LOGO! Soft Comfort V8.2.1.
2. From the menu bar select Tools → PC <-> LOGO!. The dialog opens on the Ethernet tab — close that tab mentally, do not enter an IP.
3. Click the LOGO! Cable radio button (lower-left of the dialog). The COM port selector becomes active on the right-hand pane.
4. From the COM port drop-down, select COM3 (or whatever COM number the cable enumerated as — see Section 8).
5. Click OK. The dialog switches into a "listening on COM3" state; a progress bar shows the handshake attempt.
6. Within 10 seconds the LOGO! display should switch from LOGO! <-> PC to PC <-> LOGO! with a tick — connection established.

If the dialog returns "Connection via COM port failed" after 30 seconds, the most likely cause is that the LOGO! is no longer in Transfer Mode. The 60-second timeout on the older firmware is the usual culprit. Re-execute Section 6 and click Refresh in the dialog.

8. Verifying the COM Port Number

The LOGO! PC cable's enumerated COM number is not always 3. On Windows 10/11, check it as follows.

1. Plug the cable into a USB port. The Windows device chime plays; the LED on the LOGO!-side connector lights blue (current USB cable) or green (legacy RS232 cable).
2. Open Device Manager (devmgmt.msc).
3. Expand Ports (COM & LPT). Look for Siemens LOGO! PC cable (COMx) or USB Serial Port (COMx).
4. The number x is the port to use in Section 7.

If no device appears, the cable driver is missing. The current cable ships with a WinUSB-compatible driver; Windows Update should install it within 60 seconds. For older cables, install the VCP driver package from the cable's documentation; the official driver is available through the Siemens Industry Online Support entry under the cable's MLFB.

9. Program Upload (Read) and Download (Write) Workflow

Once the dialog reports a successful handshake, the four transfer actions are exposed on the right-hand pane:

For the field case (a UV insolator with intermittent stability), the correct first action is Read from LOGO!. This is non-destructive: it does not change the running program; it copies the current ladder/FBD into the PC. The read completes in 3 to 12 seconds depending on program size. Once the project is on the PC, save it to disk as .lsc and version it.

10. Verification Checklist

After the program is read or written, perform the following checks before leaving the cabinet:

1. LOGO! display returns to the default time/date screen — confirms the handshake released cleanly.
2. LOGO! is in Run (green LED on the front, not the red Stop LED) — confirms the program is executing.
3. All inputs on the LOGO! display match the field wiring — for the 12/24 RCE variant, the four digital inputs (I1..I4) and the four analog inputs (AI1..AI4, shared with I1..I4) should show the same state in the LOGO! > Variables menu as in the field.
4. LOGO! Soft > Tools > PC <-> LOGO! closes without an error banner — confirms the COM port was released cleanly. A "Port still in use" warning usually points to a missing OK click in the dialog.
5. File hash matches — after Read, save the .lsc, then in LOGO! Soft, open File → Project Info and note the MD5/SHA. After Write to a fresh module, re-read and compare. Identical hashes prove a clean round-trip.

11. Common Pitfalls and Error Matrix

12. Migrating the Program to a Newer LOGO! (8.3 or Ethernet-enabled)

field reports ended with a successful read of the program from the aging 6ED1052-1HB00-0BHA4 and a planned migration to a new LOGO! with Ethernet. The workflow is as follows.

1. In LOGO! Soft V8.2.1, open the .lsc you read in Section 9.
2. Check the Project → Properties → Target dropdown. The base module should read "LOGO! 8 (12/24 RCE)" or close.
3. If the new module is a LOGO! 8.3 (MLFB 6ED1052-1HB08-0BA0 or later), install LOGO! Soft Comfort V8.3.0 (or later) — the V8.2.1 editor cannot target the 8.3 firmware's expanded memory map.
4. Open the .lsc in V8.3 and accept the migration prompt. The library of function blocks is largely forward-compatible; differences are limited to a few added blocks (astronomical clock, math error detection) that downgrade gracefully.
5. On the new module, repeat Section 6 to enter Transfer Mode. Plug an Ethernet patch cable directly between the PC and the new module (the new module is now used with Ethernet, so the workflow in Section 7 changes: the dialog stays on the Ethernet tab, and the IP is 192.168.0.5 by default).
6. Press Write to LOGO!. The new module is now the live controller.
7. De-energise and remove the 6ED1052-1HB00-0BHA4. Retain it as a spare for at least 12 months — Siemens typically marks older generations as phase-out for a minimum of one year after the successor's release.

13. Recovering From a Lost Password

If the LOGO! has program password protection enabled and the password has been lost, recovery is destructive. The only officially documented method is a factory reset, which erases the program and the password. The procedure on the 6ED1052-1HB00-0BHA4 is:

1. Power off the LOGO!.
2. Hold down all four arrow keys (← ↑ ↓ →) simultaneously.
3. Apply power. The display shows Reset?.
4. Press Yes (or → then OK depending on firmware). The LOGO! clears to factory defaults.

After the reset, repeat Sections 6 to 9 to re-upload a known-good program. There is no Siemens-supported password recovery service for the LOGO! line — the device is designed to be physically accessible for this reason.

14. Field-Proven Tips for the UV Insolator Case

• Take a .lsc backup before opening the cabinet door. The cabinet environment is hot (UV lamp heat) and the cable insertion can sometimes cause the LOGO! to brown-out briefly — losing the in-RAM state but not the flash program.
• After the read, compare the program size in File → Project Info → Program Memory against the 8.1 ceiling of 8 000 bytes / 400 blocks. If the program is at 7 900 bytes, the LOGO! is at its limit and a migration should be scheduled.
• For intermittent stability, the LOGO! cable method has the advantage of being local — you are not relying on the plant network. If the UV insolator is on a VLAN that you cannot reach from the engineering workstation, the serial path is the only option.
• When transferring, do not unplug the cable while the dialog is still in the "writing" state. The flash write takes 5 to 10 seconds; interrupting it bricks the LOGO! in the sense that the next power-up will start in PC-STOP mode with an empty program. Recovery is the Section 13 reset, followed by re-flash.

15. Connection Topology Reference

Figure 2 — Topology of a serial upload/download session.

16. Frequently Asked Questions