LOGO! 8 OBA8 Network I/O Configuration: TSAP and S7 Access Setup

Overview

Siemens LOGO! 8 (order-code suffix 0BA8) is the first generation of the LOGO! line to ship with a built-in Ethernet interface on the basic module. That interface turns the LOGO! into a peer on an industrial or office LAN and exposes an S7 communication stack that other LOGO! 8 controllers, S7-1200/S7-1500 CPUs, OPC UA gateways, and Modbus TCP masters can read from and write to. Configuring peer-to-peer exchange between two LOGO! 8 devices — sending a bit from device A to light a load on device B — is the most common first step into that capability.

This reference walks through every parameter the engineer controls: IP address, subnet mask, default gateway, local and remote TSAP, the network input/output (NI/NQ) objects, the "Allow S7 Access" / "Allow Modbus access" property introduced in LOGO! Soft Comfort V8.3, and the function-block paths that can drive a network output. It is written against firmware 0BA8 (LOGO! 8.x) and LOGO! Soft Comfort V8.3/V8.4.

Prerequisites

Before touching TSAP values, confirm the following.

• Hardware. Two LOGO! 8 basic modules with the Ethernet RJ45 port. The LOGO! 8.3 generation is identified by an order number ending in 0BA1 or later on the 12/24 RCE variants (e.g., 6ED1052-1MD08-0BA1). Hardware ending in 0BA0 typically runs LOGO! 8.0/8.1 firmware.
• Firmware. Both controllers should run the same or a compatible firmware branch. Mixing 8.0 and 8.3 in a peer link is supported; mixing 0BA7 (LOGO! 7) with 0BA8 is not, because LOGO! 7 has no Ethernet interface on the basic module.
• Software. LOGO! Soft Comfort V8.3 (or later) installed on a Windows PC. The PC only needs the software for commissioning; the running program is downloaded once and lives in the LOGO! itself.
• Network. A 100 Mbit/s Ethernet switch or a small office router. The two LOGO! 8 controllers plus the engineering PC all connect to the same subnet. Crossover is not required; the LOGO! Ethernet port supports Auto-MDI/X.
• IP plan. A documented IP address for each LOGO! and for the engineering PC, on the same subnet. Example: LOGO! #1 = 192.168.0.10, LOGO! #2 = 192.168.0.11, PC = 192.168.0.100, subnet mask 255.255.255.0.

Network I/O Architecture and Limits

LOGO! 8 exposes two parallel I/O surfaces to the program editor:

• Local I/O — the physical digital inputs (I1…I24) and outputs (Q1…Q20) wired to terminals on the basic module and any attached expansion modules. These never leave the device.
• Network I/O — virtual inputs and outputs delivered over Ethernet. Network inputs (NI) act like read-only local inputs; network outputs (NQ) act like write-only local outputs. The ladder/FBD block diagram can read NIs and write NQs exactly the way it reads I and writes Q.

Concrete limits in firmware 0BA8:

Each NI is a point in the remote device's memory. When you place NI1 in a contact and connect it to LOGO! #2 (192.168.0.11, TSAP 01.00), the LOGO! #1 ladder reads bit 1 from the remote output table of LOGO! #2. Conversely, when the LOGO! #1 program drives NQ3 high, LOGO! #2 sees NI3 become true on its own ladder, provided it has NI3 configured to read from LOGO! #1 at the matching TSAP.

IP Address Configuration

Each LOGO! 8 ships with DHCP enabled by default. For a deterministic two-device link, set static addresses from the LOGO! menu or from LOGO! Soft Comfort.

From the LOGO! onboard menu

1. On the LOGO! display, press ESC to enter the menu, navigate to Network.
2. Select IP Address and enter the four octets with the cursor keys.
3. Set Subnet Mask (typical 255.255.255.0).
4. Set Gateway to the router address if the LOGO! needs to talk to anything outside its subnet (e.g., a cloud gateway on 192.168.0.1). For a flat peer link on a single switch, the gateway may be left at 0.0.0.0.

From LOGO! Soft Comfort

1. Open the project for LOGO! #1.
2. Menu: Tools → Ethernet Connections (or File → Properties → Communication in V8.3+).
3. Click IP Address and enter the static address. Mark Use static IP to override DHCP.
4. Repeat for LOGO! #2 with its own address.

TSAP and Connection Parameters

The TSAP (Transport Service Access Point) is the S7 communication addressing field that sits below the IP address. On LOGO! 8, every S7 partner pair is identified by a two-byte local TSAP and a two-byte remote TSAP. The two values are written as four hex characters in the format xx.yy.

TSAP convention for LOGO! peer links

Other commonly seen values in shipped projects:

• 02.00 / 03.00 — used when LOGO! #1 must talk to two separate partners and you need to disambiguate the passive side.
• 01.01, 01.02 — the second byte is the S7 connection slot; LOGO! 8 supports up to 8 S7 connections per device. Keep slot IDs unique on the same partner to avoid collisions.

Two hard rules:

1. Local TSAP and remote TSAP must differ on the same device. The S7 stack rejects an attempt to bind to the same TSAP twice. So LOGO! #1 with local TSAP 00.00 cannot also have remote TSAP 00.00 on a second connection to the same partner.
2. Local TSAP on device A must equal remote TSAP on device B and vice versa. This is what the four numbers actually mean: "I am reachable as 00.00, I want to talk to 01.00."

Where to enter TSAP in LOGO! Soft Comfort

1. Open the project.
2. Menu: Tools → Ethernet Connections.
3. In the connection table, click the row that represents the peer link. The Local TSAP and Partner TSAP columns are editable.
4. Enter the values per the convention above and click Apply.

Creating the Network Link in LOGO! Soft Comfort

The "draw a connection between the two diagrams" workflow is the visual configuration of an Ethernet connection. It is what tells Soft Comfort which NI/NQ points cross the wire and what addresses they should resolve to. The link is configured on the program that owns the NQ (the sender) and the program that owns the NI (the receiver).

Step-by-step: sender program (LOGO! #1)

1. In LOGO! Soft Comfort open the program for LOGO! #1 (the device that will write to the remote output).
2. Drag a Network Output block from the connector list onto the diagram. By default LOGO! Soft Comfort places NQ1.
3. Open Tools → Ethernet Connections. The connection table is initially empty.
4. Right-click the table and select Add Connection. Choose S7 Connection.
5. Fill in:
   • Partner IP Address = 192.168.0.11 (LOGO! #2)
   • Local TSAP = 00.00
   • Partner TSAP = 01.00
   • Connection Name = a descriptive string (e.g., "to_LOGO2_light")
6. Click Apply. The NQ1 block in the diagram now resolves to a write operation against the partner address.
7. Save and download to LOGO! #1.

Step-by-step: receiver program (LOGO! #2)

1. Drag a Network Input block (NI) onto the diagram, defaulting to NI1.
2. Open Tools → Ethernet Connections and add a connection with:
   • Partner IP Address = 192.168.0.10 (LOGO! #1)
   • Local TSAP = 01.00
   • Partner TSAP = 00.00
3. Wire NI1 to the Q1 output coil in the diagram (the physical light).
4. Save and download to LOGO! #2.

Driving Network Outputs from Function Blocks

An NI/NQ can be sourced from any block that produces a Boolean or analog output. Common patterns:

Boolean network output driven by a function block

1. Place the function block — for example a Weekly Timer (B001) or a Up/Down Counter (C001) — and bring its Boolean output to a temporary marker M1.
2. Wire M1 to the input of an NQ block. The connection is a single click on the connector and a single click on the NQ input.
3. The NQ now toggles in step with the function block's logic. No additional glue logic is required.

Analog network output from an arithmetic block

1. Place an Analog Amplifier or Math block whose output is a 16-bit value.
2. Wire that output to a Network Analog Output (NAQ1…NAQ32).
3. On the partner LOGO!, place a Network Analog Input (NAI1…NAI32) bound to the same connection. The analog value appears in the remote ladder as a normal analog tag and can be wired to a comparator, display, or PID block.

Edge cases and gotchas

• Coil vs. contact semantics. An NI behaves like a contact — it is a read-only Boolean. An NQ behaves like a coil — it accepts a Boolean drive. The editor will let you wire them either way; verify by hovering the tooltip before commissioning.
• Marker scope. A local marker M is not network-visible. To make a value network-visible, place it on an NQ coil. Sharing an M to a partner has no effect.
• Retain. Retain bits and markers are local-only on LOGO! 8. NQ values are not retained across a power cycle on the remote partner; if you need a retained handshake, latch the bit locally on the remote side after reading it from NI.
• Scan ordering. NI/NQ values are updated at the end of each LOGO! cycle, so a one-cycle latency is normal. Do not expect NI to reflect an NQ that was set in the same scan on the partner.

Access Protection on LOGO! 8.3 and Later

Firmware 8.3 and the matching LOGO! Soft Comfort V8.3 introduced an access-control property that did not exist in earlier 0BA8 firmware. When the property is left at its default (denied), the LOGO! 8 silently drops every S7 read/write and every Modbus request, even when the IP and TSAP are perfectly correct. This is the single most common cause of a peer link that compiles, downloads, and shows the connection as "Established" in the Ethernet table — yet returns zeros at runtime.

How to enable access

1. Open the project in LOGO! Soft Comfort V8.3 or later.
2. Menu: File → Properties.
3. In the General tab, locate the Access Protection group.
4. Tick Allow S7 Access to permit peer S7 communication (which is what an NI/NQ link uses).
5. Tick Allow Modbus Access if the LOGO! is also being polled by a Modbus TCP master (HMI, SCADA, third-party gateway).
6. Click OK and re-download the program to the LOGO!.

Why the property exists

Before 8.3, any host on the network could read and write LOGO! memory with no password. The access property closes that hole without requiring a full user management system; it is a single bit per protocol. In a production deployment, leave the property off by default and enable it only on the LOGO!s that need to participate in a peer link or be polled by a master.

Router and Network Considerations

When the two LOGO!s sit behind a router rather than on a single switch, a few extra constraints apply.

• Same subnet, different switch. As long as both LOGO!s have IP addresses on the same subnet and the device in the middle functions as a Layer 2 device (a switch with VLAN routing, or a flat consumer router in default config), the S7 connection goes through transparently. The "default gateway" field can be left at 0.0.0.0 if no traffic is destined off-subnet.
• Different subnets, true router in the middle. Set the default gateway on each LOGO! to the router's interface address in its own subnet. S7 communication across routed boundaries generally works, but connection setup time increases and the connection is more sensitive to keep-alive timeouts.
• Firewall. S7 communication uses TCP port 102. Ensure any firewall on the engineering PC or on the router does not block port 102 between the two LOGO! subnets. Modbus TCP uses port 502; the LOGO! web server uses port 80.
• Discovery broadcasts. LOGO! Soft Comfort uses UDP broadcast (typically port 1025) for online discovery. If the router blocks broadcast, the LOGO! will not show up in the Online → Select Target dialog, but you can still connect by typing the IP address manually in the target dialog.

Verification and Diagnostics

After downloading, verify the link in this order.

1. Ethernet connection status. In LOGO! Soft Comfort, open Tools → Ethernet Connections. The connection row should show a green status indicator. A yellow indicator means the connection is configured but not yet established; a red indicator means configuration error.
2. Online monitor. Switch to Online → Online Test mode. The NI/NQ blocks display live values. The NQ coil in LOGO! #1 should show the value being driven; the NI contact in LOGO! #2 should mirror it.
3. Web server. LOGO! 8 has a built-in web server on port 80. Browse to http://192.168.0.10 from the engineering PC. The home page shows the LOGO!'s IP, MAC, firmware version, and a tabbed view of I, Q, M, NI, and NQ. You can watch NQ values toggle in real time without writing any code. On firmware 8.3+, the web server itself can be disabled; if the page will not load, check the "Allow Web Server Access" property in File → Properties → General.
4. Onboard display. On a LOGO! with a built-in display (…RCE variants), press ESC → Network → Connections. Each S7 connection is listed with state (Active / Idle / Error).
5. LED. The Ethernet LED on the RJ45 jack lights solid when a physical link is present and blinks with traffic. A persistent dark LED means a physical-layer problem (cable, switch port, wrong pinout).
6. Ping test. From the engineering PC, ping each LOGO! IP. A reachable IP with no S7 traffic usually points to a TSAP or access-property problem. An unreachable IP points to Layer 2/3 configuration.

Troubleshooting Matrix

For the most recent firmware files, LOGO! Soft Comfort installers, and the LOGO! 8 system manual, refer to the Siemens LOGO! product page and the Siemens Industry Online Support portal.

FAQ