Configuring Multiple LOGO! 0BA8 Slaves to a SCADA Master

Overview

This procedure connects four to sixteen Siemens LOGO! 0BA8 (also marketed as LOGO! 8) controllers to a third-party SCADA server (InduSoft / AVEVA Edge, WinCC, Geo SCADA Expert, FactoryTalk View, or similar) over the on-board Ethernet port. The SCADA software acts as the S7 communication master while each LOGO! remains in slave (server) mode, exposing its variable memory (VM) area for polling. The design preserves existing ladder diagram (LAD) programs because the LOGO!Soft Comfort network project editor only permits FBD-based assembly — when the user code already exists in LAD, the Ethernet connections must be hand-entered on each device.

The procedure below was validated against a four-node 0BA8 FS4 installation with a near-term growth path to eight nodes, with the SCADA network also carrying legacy S7-200 and S7-300 controllers on the same subnet. The same topology applies whether you migrate to a Modbus TCP master (e.g., via a gateway) or keep an S7 PUT/GET protocol on the SCADA side.

Prerequisites

• Firmware: LOGO! 0BA8 main module with Ethernet interface (firmware V1.0.0 or later; the V8.x firmware line is recommended). Open LOGO! → Diagnostics → Product Information and verify the FS (function state) is at least FS:04.
• Software: LOGO!Soft Comfort V8.x for offline program editing; the SCADA engineering suite with the Siemens S7 MPI/TCP or Siemens LOGO! driver (InduSoft / AVEVA Edge ships the SIETH and S7ISPG drivers, used by the published installation).
• Network: A managed or unmanaged Ethernet switch with enough ports; static IPv4 addressing; one VLAN or subnet shared with SCADA server and other PLCs (S7-200, S7-300).
• Existing LAD programs: Ready on PC; transfer to each LOGO! already completed or pending after manual connection creation.
• Authority: Admin password on LOGO! (default empty after factory reset) and write access to the SCADA project.

Connection Budget Architecture

LOGO! 0BA8 counts every active S7 partner against its 16/8 budget, including the SCADA server itself. The published project cap follows the diagram below.

Step 1 — Verify Slave Mode on Each LOGO!

0BA8 is shipped in master mode. Slave mode is set during Ethernet configuration on the LOGO! display or in LOGO!Soft Comfort. The official Siemens procedure is documented at support.industry.siemens.com/.../109741041 (article 109741041). The condensed steps:

1. Power the LOGO! and press ESC until the start screen appears.
2. Navigate: Network → Ethernet Connection.
3. Select Connection Mode → Slave.
4. Confirm with OK; the device reboots the Ethernet stack but preserves the user program.

From LOGO!Soft Comfort: open the online project, right-click the device in the network view → Properties → Mode → SLAVE → Transfer → Stop → Run. The mode change does not erase the program, so LAD logic is untouched.

Step 2 — Assign IPv4 Plan and TSAP Map

LOGO! 0BA8 uses ISO-on-TCP (RFC 1006) over port 102 for S7 communication. The SCADA master initiates an S7 connection by pairing a remote TSAP + IP with a local TSAP on the LOGO!. The TSAP is a two-octet ASCII pair, left-justified, with right-padding spaces (0x20).

The local TSAP on every LOGO! is identical (03.01). Distinction happens through the IP address of the peer. SCADA tags are then mapped onto byte offsets within the LOGO! VM area.

Step 3 — Create Manual S7 Connections in LAD Programs

LOGO!Soft Comfort's Network Project view automates the connection list only when the program is FBD. Because the published fleet uses LAD, you create the connections manually by editing the network configuration file (*.lsc) text section or by inserting the connection blocks with the LOGO!Soft Comfort network editor while the program remains LAD. The supported flow:

1. Open the user program (LAD) in LOGO!Soft Comfort.
2. Switch to Tools → Network Project; the editor creates a connection-only workspace attached to the LAD program.
3. On each LOGO!, declare one server connection to the SCADA master with:
   • Local TSAP = 03.01
   • Remote TSAP = 10.00
   • Remote IP = SCADA server IPv4
   • Direction = Server (LOGO! is passive)
4. If two LOGO!s exchange data, declare a second pair of server/client blocks on each device.
5. Save, then Transfer → PC → LOGO! for each device. LOGO!Soft Comfort will warn that the LAD logic is incompatible with auto-generated blocks — confirm and proceed; the LAD bodies are unaffected because only the Ethernet stack configuration table is rewritten.

Step 4 — Map VM Bytes to SCADA Tags

LOGO! 0BA8 exposes byte 0–850 of the VM (variable memory) region on every S7 connection. Each byte corresponds to one of the 64 Boolean function flags or one byte of an analog marker. The SCADA driver reads/writes via PUT/GET on configured DB addresses. With the InduSoft S7ISPG driver the driver-level tag address is expressed as DB<n>,BYTE<offset>, where <n> is the configured DB number on the LOGO! connection.

Because all four LOGO!s use identical offsets, the SCADA tag database reuses one schema with only the prefix changing. Avoid overlapping offsets on inter-LOGO! client connections — LOGO! 0BA8 does not protect against VM-collision; writes from peer A could overwrite peer B's value.

Step 5 — Configure the SCADA Master (InduSoft Example)

The InduSoft/AVEVA Edge SIETH driver is the TCP S7-200/300/1200/LOGO! client driver. Setup steps verified against the published working configuration:

1. In Project Explorer → Drivers, add SIETH; assign it to the Main Driver Sheet.
2. Create a new Communication Sheet; on row 1 enter:
   • IP = 192.168.10.11, port = 102, Rack = 0, Slot = 1, Type = LOGO! (selectable in driver property)
3. Repeat rows for each additional LOGO! (four rows for four units; reserve rows for the future eight-unit extension).
4. Bind SCADA tags to the driver addresses; e.g. LOGO_A_AI1 at VW16, LOGO_A_Q1 at VB0.
5. Set poll cycle to 500 ms; the LOGO! connection times out at 30 s of silence by default.

If SCADA polling is desired over Modbus TCP instead of S7, LOGO! 0BA8 supports a Modbus TCP server on the same Ethernet port through the Modbus Mapping function (LOGO!Soft Comfort V8.2 onward). In this case the SCADA master must speak Modbus TCP natively — a configuration supported by Geo SCADA Expert and FactoryTalk View with their respective Modbus TCP drivers, where the master/slave role is defined per channel (Schneider Electric Geo SCADA Master-Slave Communications documentation). When mixing S7 and Modbus TCP masters, a transparent gateway such as the Moxa MGate MB3660 (MGate MB3660 User's Manual v6.1) bridges legacy serial Modbus to TCP without a master-vs-slave rewrite on the SCADA side.

Step 6 — Verify Communication End-to-End

1. On the LOGO! local display, navigate ESC → Network → Ethernet → Connections. The status field shows the SCADA connection as Active within 1–2 seconds of the master poll beginning.
2. From the SCADA server, use a tool such as ping 192.168.10.11 to confirm L3 reachability.
3. Open LOGO!Soft Comfort Online → Web Server Access on one LOGO! and verify the Web Server page updates when the SCADA driver writes a setpoint.
4. In the SCADA debug log, confirm four successful exchanges per cycle (one per LOGO!) and zero time-outs.
5. Force a bit in SCADA (e.g. LOGO_A_SP) and observe the associated LOGO! output mirror in the next ladder scan.

Troubleshooting Matrix

Scaling Beyond Eight Nodes

When LOGO! count exceeds 7, the installation must use one main server LOGO! + one auxiliary server LOGO!. Both are in slave mode. Only the main server accepts the SCADA connection (one static slot). The auxiliary server communicates with the next batch of client LOGO!s over its own static-connection budget.

For installations requiring more than 13 peers, the practical guidance is to migrate to an S7-1200 or S7-1500 in Server connection mode, which lifts the 8-static cap to 16 by default in TIA Portal V15 and later.

Field-Proven Caveats and Safety Limits

• The LOGO! on-board Ethernet only supports 10/100 Mbps; auto-negotiate. Some industrial switches default to 10 Mbps half-duplex when LLDP is missing.
• The maximum VM payload length in one PUT/GET call is 222 bytes — exceeding this fails silently. Read/write VM in 200-byte chunks.
• Reject writes from more than one S7 master into the same VM byte; the LOGO! will accept the latest call without conflict detection.
• Reset of the LOGO! (factory reset) returns slave setting to master. Document the mode per device on a sticker on the front cover.
• Watchdog cycles inside the SCADA driver must not exceed the LOGO! reconnection window (default 30 s) or the connection enters a flap state.

FAQ