Configuring S7-1500 to LOGO! 8 S7 Communication and DB Addressing

Problem Overview: S7-1500 to LOGO! 8 Communication Failure

Field installations pairing a SIMATIC S7-1500 CPU 1511-1 PN with a LOGO! 8 (0BA8 / FS4) frequently fail with "Remote address invalid," "Connection cannot be established," or with the client/server mismatch where the data block (DB) shows no online values despite a green connection LED. The failure is rarely a hardware defect; it is almost always caused by one of three configuration issues:

1. Wrong DB absolute addressing syntax (DB1.DB0 vs. DB1.DBB0).
2. Incorrect assignment of the S7 communication role (LOGO! 8 must be the S7 client, the S7-1500 must be the S7 server).
3. Missing "Permit access with PUT/GET communication" protection setting on the S7-1500 CPU.

Combined with the LOGO! 8 requirement that analog process values be routed through an Amplify (B081) block to the Variable Memory (VM) area, these issues are resolved by following the procedure below.

Tested Hardware and Software Baseline

Refer to the Siemens S7-1500 CPU 1511-1 PN manual (entry ID 109751786) and the LOGO! 8 system manual (entry ID 100761982) for the authoritative hardware reference.

Network Topology

The reference topology is a point-to-point Ethernet link on a shared /24 subnet. The S7-1500 and the LOGO! 8 must be on the same subnet with no routing required for the S7 connection.

• S7-1500 CPU 1511-1 PN — IP 192.168.0.1 / mask 255.255.255.0
• LOGO! 8 (FS4) — IP 192.168.0.2 / mask 255.255.255.0
• Default S7 communication port: TCP 102

Root Cause 1 — Wrong Absolute DB Address Syntax

S7-1500 absolute addressing requires an explicit data type prefix that the LOGO! 8 S7 client transmits in the PUT/GET request:

The string DB1.DB0 is not a valid S7 absolute address and is rejected by the CPU with a "remote address invalid" diagnostic event. Always specify DBB / DBW / DBD / DBX. When configured through the LOGO! Soft Comfort Ethernet connection wizard, the address field is byte-oriented; the wizard appends the byte width automatically. If you are entering the address manually, use the byte form DB1.DBB0 for single-byte transfers.

Root Cause 2 — S7 Client / Server Role Assignment

LOGO! 8 (0BA8 / FS4) implements the S7 communication protocol as a client only. The S7-1500 acts as the server, listening on TCP 102 and accepting PUT/GET requests. Configuring the S7-1500 as the S7 client (using TSEND_C / TRCV_C or the PUT/GET instruction with the LOGO! as the partner) causes the connection to come up but no data is exchanged — the LOGO! 8 will not accept an unsolicited PUT/GET from a peer that is not the configured server.

From the S7-1500 side this means the CPU only needs to expose a server connection; no active PUT/GET block has to be programmed. The S7-1500 protection setting "Permit access with PUT/GET communication from remote partner" must be enabled — see the next section.

Root Cause 3 — Missing PUT/GET Access Permission on the S7-1500

Starting with firmware V1.8 the S7-1500 CPU blocks all PUT/GET access by default as a security hardening measure. The setting is located in TIA Portal under:

Project tree → CPU 1511-1 PN → Properties → Protection & Security → Connection mechanisms → Permit access with PUT/GET communication from remote partner (must be checked)

With the option cleared, the S7-1500 silently rejects PUT/GET requests from the LOGO! 8 S7 client. Confirm the tickbox is enabled and download the hardware configuration to the CPU before re-attempting the connection.

Step-by-Step Configuration Procedure

Prerequisites

• Both devices powered and reachable by ping on the same subnet.
• LOGO! 8 base module with Ethernet (e.g., 6ED1052-1CC00-0BA8).
• TIA Portal V13 SP1 or higher installed; LOGO! Soft Comfort 8 or higher installed.
• Empty DB1 in the S7-1500 program (created with "Standard access" or "Optimized" — note: PUT/GET with LOGO! 8 is most reliable with a non-optimized DB, see TIA Portal S7-1500 manual section 4.7).

Step 1 — Configure the S7-1500 server side

1. Open TIA Portal → open your project containing the CPU 1511-1 PN.
2. Create a new global DB (e.g., DB1 "LOGO_Interface") with the byte-aligned tags you need to exchange. Disable "Optimized block access" on the DB properties so the absolute addresses are byte-addressable.
3. Navigate to CPU 1511-1 PN → Properties → Protection & Security → Connection mechanisms and check Permit access with PUT/GET communication from remote partner.
4. Compile the hardware configuration and download to the CPU.
5. Note the S7-1500 IP address and rack/slot (0 / 1 for the 1511-1 PN).

Step 2 — Configure the LOGO! 8 S7 client

1. Open LOGO! Soft Comfort 8 and load the project (or create a new one).
2. From the menu bar select Tools → Ethernet Connections (or LOGO! → Ethernet Connections in older builds).
3. Add a new S7 connection. Fill in the parameters:

4. Compile and download the program to the LOGO! 8. Cycle power if prompted.
5. In Online → Ethernet Connections → Test, the connection should transition to Established.

Step 3 — Route analog values through Amplify to VM

The LOGO! 8 S7 client can only read from the LOGO! variable memory (VM) area, not from the marker (M) area. The mapping is:

For an analog input (e.g., AI1 = 0–10 V) you must insert an Amplify (B081) block between the analog input and the VM destination:

1. From the LOGO! Soft Comfort toolbox, drag the Amplify block onto the diagram.
2. Connect the analog input to the Amplify input.
3. Set the gain and offset so the output represents the engineering range (e.g., 0.0 to 100.0 °C for a PT100).
4. Connect the Amplify output to a VM word (e.g., VW0).
5. Map the VM word to DB1.DBB0 / DB1.DBW0 in the S7-1500.

Verification Procedure

1. In TIA Portal, right-click the S7-1500 → Go online.
2. Open DB1 and click the "Monitor all" (glasses) icon.
3. The byte/word values at DB1.DBB0 (or whichever offset you configured) should update at the LOGO! 8 update cycle — typically 250 ms to 1 s, depending on the LOGO! program cycle time.
4. In LOGO! Soft Comfort, switch to Online Test and watch the VM word update with the same value.
5. Force a value into the LOGO! 8 VM (e.g., set the Amplify output to 50.0) and confirm the corresponding DB1.DBB value changes on the S7-1500 side.

Troubleshooting Matrix

The third-party library S7NetPlus issue #179 documents the same client/server limitation — third-party .NET S7 stacks can only talk to the LOGO! 8 by pretending to be a S7-1500/300/400 server, which is not possible. Treat the LOGO! 8 strictly as an S7 client.

Security and Firmware Notes

• Firmware V1.8 on the CPU 1511-1 PN is end-of-life. Siemens recommends firmware V2.0 or higher. The PUT/GET access path is preserved across all firmware versions but the menu location for the toggle is identical.
• For new projects, use a non-optimized (standard) DB for the LOGO! interface DB. Optimized DBs are still readable through PUT/GET but the address mapping may be non-contiguous, leading to byte-order issues when exchanging 16-bit values with the LOGO! 8 (big-endian on LOGO! side, little-endian on S7-1500 side).
• Always lock the LOGO! 8 Web Server with a password if the device is exposed to a non-isolated network. The default Web Server password is empty and exposes the VM area read-only.

Performance and Cycle Time

LOGO! 8 runs the user program on a fixed cycle of 250 ms by default (fast scan is 50 ms for a subset of FBs). Each S7 connection is serviced in that cycle. Practical throughput:

• Single S7 connection: ~4 reads/sec from VM to S7-1500 DB.
• Maximum 8 S7 / Modbus TCP connections in parallel per LOGO! 8 base module.
• Total transfer size: up to 32 bytes per S7 read/write request in standard configuration.

These limits are hard caps in the LOGO! 8 firmware and apply regardless of TIA Portal or LOGO! Soft Comfort version. If higher throughput is required, replace the LOGO! 8 with an S7-1200 or ET 200SP.

Alternative: Modbus TCP Instead of S7 Communication

If the S7-1500 → LOGO! 8 link proves unstable on certain firmware combinations, an alternative is to use Modbus TCP on the LOGO! 8 side and the S7-1500 as Modbus TCP client. The LOGO! 8 supports Modbus TCP server mode natively (Function Codes 03 / 06 / 16) on the same Ethernet port 502. The S7-1500 can use the MB_CLIENT instruction from the TIA Portal library. This approach is sometimes more stable on older LOGO! 8 firmware revisions and avoids the PUT/GET protection toggle. Refer to the LOGO! 8 system manual Modbus chapter.