Resolving S7-1200 to LOGO! 0BA7 Network Error Communication

When a Siemens S7-1200 CPU is connected to a LOGO! 0BA7 (LOGO! 8 generation) over Ethernet, the LOGO! display occasionally shows Network error under Diagnostic and Error info. The S7-1200 can be pinged and programmed from the engineering PC, the LOGO! can be reached by ping and from LOGO!Soft Comfort (LSC), but the digital signal the S7-1200 is supposed to send never reaches the LOGO! logic. This reference documents the root cause, the official Siemens application example, and the field-proven correction steps for TIA Portal V13 / LSC V7.1.5 deployments using a SCALANCE XB005 unmanaged switch.

1. System Overview

The reference topology uses four Ethernet nodes on a single 192.168.0.0/24 subnet terminated on an unmanaged Siemens industrial switch:

The S7-1200 is the S7 server. The LOGO! 0BA7 is the S7 client and actively establishes the TCP connection to the controller. The HMI is a passive viewer and the PC is the engineering station. All S7 payload originates on the S7-1200 and is consumed by LOGO! 0BA7 through its Network Input (NI) symbols.

2. Hardware Reference

The unmanaged SCALANCE XB005 (SCALANCE XB-000 product manual) is the most common field installation. It requires no configuration but does not provide diagnostics, so a Network error message must be diagnosed from the S7-1200 and LOGO! ends of the link.

3. Problem Symptom and Root Cause

Symptom reported in the field:

• LOGO! display: Network error under Diagnostic and Error info.
• LOGO! does not react to a digital bit toggled in the S7-1200 data block.
• ICMP ping from PC to 192.168.0.1 and 192.168.0.11 succeeds (4/4 packets).
• LSC online connection to the LOGO! works.
• TIA Portal online connection to the S7-1200 works.

Three root causes account for nearly all Network error messages on a 0BA7 acting as an S7 client:

1. PUT/GET access is disabled on the S7-1200. The default security profile of an S7-1200 (and S7-1500) blocks PUT/GET communication from a remote partner. The connection is established at TCP level but the controller rejects the S7 read/write services, which the LOGO! reports as a generic Network error.
2. Wrong memory area consumed in LSC. The LSC program uses a digital input (Ix) as the sink for the S7 data. Digital inputs on LOGO! are physically driven only by the terminal block; the CPU overwrites them every scan. Network data must be written to the V (Variable) area and consumed through a Network Input block (NI).
3. TSAP or partner mismatch. The TSAP of the LOGO! Ethernet connection in LSC does not match the S7-1200 connection resource. The default local TSAP of an S7-1200 CPU slot 1 is 01.00; the LOGO! must point at this value.

4. Prerequisites

• TIA Portal V13 SP1 or higher with STEP 7 Basic and WinCC Basic installed.
• LOGO!Soft Comfort V7.1.5 or compatible (V8.0+ recommended for current firmware).
• S7-1200 firmware V4.0 or higher (V4.2 recommended).
• LOGO! 0BA7 firmware ES8 (or current 0BA8 / 0BA7 update level).
• All four nodes on the same subnet / VLAN, MTU 1500.
• Reference manual: LOGO! Client to S7 Server S7 Communication (Siemens application example, 109778776).
• LOGO! 0BA7 system manual: LOGO! 8 system manual (109741041).
• S7-1200 system manual: SIMATIC S7-1200 programmable controller system manual (109772940).

5. Step-by-Step TIA Portal V13 Configuration

5.1 Build the project and add the S7-1200

1. Open TIA Portal, create a new project, switch to the Project view.
2. Add a CPU 1215C DC/DC/RLY from the hardware catalog. Accept the default module rack.
3. Open Device configuration > Ethernet address and set:
   IP address: 192.168.0.1
Subnet mask: 255.255.255.0
4. Compile the hardware configuration and download it.

5.2 Create the S7 connection resource (LOGO! as client)

The LOGO! is the S7 client, so the S7-1200 must publish an S7 connection slot:

1. In the S7-1200 device tree open Properties > Communication > S7 connection.
2. Confirm the default local TSAP is 01.00 (CPU slot 1). This is the partner TSAP the LOGO! must point at.
3. The S7-1200 will accept the connection when the LOGO! issues an S7 CR with local TSAP 01.00.

5.3 Enable PUT/GET remote partner access

1. Select the S7-1200 CPU in the project tree.
2. Open Properties > Protection & Security > Connection mechanisms.
3. Tick Permit access with PUT/GET communication from remote partner.
4. Download the hardware configuration. The change takes effect immediately on RUN.

5.4 Create a data block for the network bits

The S7-1200 must expose process data in a data block. The LOGO! TSAP target is a single byte that maps to a LOGO! V area byte.

1. Add a new global DB (Add new block > Data block), name it DB_S7_LOGO, untick Optimized block access.
2. Declare byte DBB0 as Byte, initial value 0.
3. In a cyclic OB (OB1) copy the digital input state into DB_S7_LOGO.DBX0.0:
   DB_S7_LOGO.DBX0.0 := I0.0;

Any bit toggled in DBB0 (8 bits, X0.0 to X0.7) will propagate 1-to-1 to the LOGO! V byte VB0 and is accessible as V0.0...V0.7 in the LOGO! program.

6. Critical Configuration: V Memory, Network Input, PUT/GET Permission

6.1 LOGO! 0BA7 memory map

6.2 Why I does not work but V does

LOGO! 0BA7 refreshes its physical digital inputs from the terminal block at the start of every scan. Any value the S7-1200 writes to Ix.y is overwritten on the next cycle. The LSC program therefore never sees a high bit. The S7-1200 must write to the V area, and the LSC program must read it through a Network Input (NI) block — never through an I contact.

6.3 Configure the Ethernet connection in LSC

1. In LOGO!Soft Comfort open Tools > Ethernet Connections (or Connection list in newer revisions).
2. Add a new S7 connection with the following parameters:
   Server IP address: 192.168.0.1 (S7-1200)
   Server TSAP: 01.00 (S7-1200 CPU slot 1)
   Client TSAP: 01.00 (LOGO! default, do not duplicate within the same network)
   Read from server (LOGO! <- S7-1200): DB3.DBB0 -> VB0
Write to server (LOGO! -> S7-1200): optional, e.g. VB10 -> DB3.DBB10
3. Tick Connection is active and Cyclic transmission if the LOGO! is to poll every cycle.
4. Transfer the LSC program to the LOGO! with PC > LOGO!.

6.4 Add the Network Input in the LSC ladder program

1. From the LSC toolbox drag a Network Input (NI) contact onto the rung.
2. Set the address to NI1. The NI block is automatically bound to the first byte of the connection, which in the configuration above is VB0.
3. Wire NI1 to the next function block (relay coil, AND, OR, etc.).

For a 1:1 digital input mapping, the binding is:

7. The "Change Device" Workaround

A second field-proven remedy reported on this specific hardware combination (S7-1200 1215C DC/DC/RLY, LSC V7.1.5, TIA V13) is to re-bind the S7-1200 CPU from inside the project:

1. In TIA Portal select the S7-1200 in the project tree.
2. Right-click > Change device > Change to same device (or Replace device > identical article number 6ES7215-1xxx40-0XB0).
3. Accept the reassignment, recompile (Hardware > Compile) and re-download to the S7-1200.

This forces a clean re-build of the connection table that ships to the S7-1200 firmware. It is the recommended last-resort fix when the configuration appears correct but the S7 connection resources on the CPU are stale (typically caused by switching between V12 and V13 projects, or by upgrading a CPU that was previously configured with a different module type). It is the equivalent of rebuilding the S7-1200 connection table from scratch without deleting the project.

8. Network Diagnostics

8.1 ICMP ping from the PC

ping 192.168.0.1   -t   (S7-1200)
ping 192.168.0.11  -t   (LOGO! 0BA7)
ping 192.168.0.2   -t   (HMI)

All three should reply with <1 ms RTT on a properly terminated copper link. Packet loss or TTL expiry indicates a Layer 1/2 issue (cable, switch port, duplex mismatch).

8.2 TIA Portal online diagnostics

1. Select the S7-1200 > Online > Online & diagnostics.
2. Open Diagnostics > Connection. Any S7 connection resource that is established will be listed with state = ESTABLISHED. If the LOGO! connection shows IDLE or is missing, the LOGO! is not opening the TCP socket.
3. Open Diagnostics > Security > Event log. A blocked PUT/GET write attempt logs a Access denied event of class Security event.

8.3 LOGO! 0BA7 display diagnostics

Navigate LOGO! display > Diagnostic and Error info > Network error to view the IP of the partner that caused the error and the timestamp. The error clears automatically once the connection re-establishes.

8.4 S7 trace with TIA Portal V13.1+

TIA V13.1 and later exposes the S7-1200 Web server on port 80 and the diagnostic buffer on port 102. If the LOGO! connection still fails after enabling PUT/GET, capture the diagnostic buffer (Online > Diagnostics > Diagnostic buffer) and look for entries with event ID 0x11 (connection aborted) or 0x13 (connection resource problem). Both indicate a TSAP or partner mismatch, not a security block.

9. Verification Procedure

1. With TIA Portal online, force DB_S7_LOGO.DBX0.0 = TRUE using the Monitor & Force table.
2. Watch the LOGO! display: navigate to Network inputs and verify NI1 bit 0 = 1.
3. Force a second bit, e.g. DBX0.3 = TRUE, and verify NI1 bit 3 = 1 on the LOGO!.
4. Force both bits back to FALSE and confirm the LOGO! follows within one scan (~50 ms at default LOGO! cycle).
5. Cycle power on the LOGO!. After boot the NI values should repopulate within 2 s (default reconnection interval of the LOGO! 0BA7 S7 client).

10. Troubleshooting Matrix

11. Field-Proven Cautions

• Optimized DB blocks on the S7-1200 cannot be the target of a partner PUT/GET. The DB used as the S7 source must be non-optimized (absolute addressing). Optimized blocks were introduced with S7-1200 V4.0 and are the default for new blocks; explicitly untick Optimized block access when creating the DB.
• Two LOGO! clients with the same TSAP will not be distinguishable to the S7-1200. The default LOGO! client TSAP is 01.00; if you commission more than one LOGO! on the same S7-1200, change the client TSAP on each unit to a unique value (01.00, 01.01, 01.02, ...).
• LOGO! 0BA7 firmware ES8 is the last update level for the 0BA7 hardware. ES8 and the later 0BA8 (LOGO! 8.1) and 0BA9 (LOGO! 8.2 / 8.3) hardware are all S7-compatible but their LSC revisions differ. A program created in LSC V7.1.5 will load into a 0BA7 and 0BA8, but a 0BA9 must use LSC V8.2 or later.
• Cable length on copper Ethernet to the SCALANCE XB005 must be <100 m per segment, 10/100 Mbit/s full duplex, with Cat 5e minimum. Industrial installations should use the Siemens IE TP Cord (6XV1850-2xxx0) with M12 D-coded or RJ45 connectors as appropriate.
• Watchdog behavior: if the S7-1200 goes to STOP, the LOGO! Network error count increments once per the LOGO! reconnection interval. This is informational, not a fault. Restart the connection by cycling the LOGO! power only if the S7-1200 stays in STOP for an extended period and the connection resource is deallocated.
• No PUT/GET on S7-1500 in safety mode: if the controller is upgraded to an S7-1500, PUT/GET must still be enabled, and in a failsafe / safety program the data exchange is subject to additional restrictions. The Siemens application example 109778776 covers both S7-1200 and S7-1500 server configurations.