Siemens LOGO! 8 Network Project: Adding a 5th Digital Output Across Two Base Modules

The Siemens LOGO! 8 base module (generation 0BA8, marketed as "LOGO! 8") is delivered with a fixed I/O map of eight digital inputs and four digital outputs. The "4-output" ceiling is set in hardware; no firmware revision of the base module exposes Q5-Q8 on the base terminals. When a fifth load must be controlled and a second LOGO! 8 is already available on the panel or in the cabinet, the cleanest path to that fifth controllable output is a network project in LOGO! Soft Comfort. The remote input on the second LOGO! is treated as if it were local, and it drives a free Q on the second base that physically powers the fifth load. This article documents the prerequisites, the FBD/LAD configuration, the IP/networking requirements, the verification steps, and the failure modes a field engineer will hit on a real installation.

1. The 4-Output Constraint of the LOGO! 8 Base Module

All 0BA8 base modules in the LOGO! 230RCE, 24RCE, 12/24RCE, and 24RCEo families share the same I/O count. The relevant catalog numbers (the family prefix 6ED1052- is constant):

The user's stated "8 DI / 4 DO" is the stock count of any 0BA8 base. There is no firmware upgrade that adds Q5 to the base terminals; Q5 and beyond only exist on the LOGO! DM8 and DM16 digital expansion modules that sit on the right-hand expansion bus.

2. Three Legitimate Paths to a 5th Output

1. Add a LOGO! DM8 digital output module (catalog 6ED1055-1MB00-0BA2 for relay, 6ED1055-1MA00-0BA2 for transistor). Adds 4 more outputs, taking the local station to 8 outputs total.
2. Add a LOGO! DM16 digital output module. Adds 8 more outputs; the local station reaches 12 outputs.
3. Network two LOGO! 8 base modules and use Network I/O. Uses the second LOGO!'s Q1-Q4 to physically drive the 5th load. No new hardware, but a deterministic Ethernet link is required.

This article is dedicated to path 3, the network I/O approach. Path 1 is preferred when the budget allows a new module and a fast response is mandatory; path 3 is preferred when a second LOGO! is already deployed.

3. Prerequisites

Refer to the Siemens Industry Online Support portal for the current LOGO! 8 system manual and the LOGO! Soft Comfort online help. The catalog prefix 6ED1052- identifies all LOGO! 8 base modules in the Siemens Industry Mall.

4. Network Project Architecture

A LOGO! 8 network project ties up to 16 LOGO! stations into one project. Each station has its own IP address and a unique station number (1-16). Inputs and outputs of one station can be exposed as Network Outputs (NQ) for the other stations to consume as Network Inputs (NI). There can be up to 64 NIs and 64 NQs per project; the 5th-output use case consumes 1 NI and 1 NQ.

4.1 Station Roles for the 5th-Output Application

• LOGO! A (source): The station that owns the digital input commanding the 5th load. In the user's words, this is the LOGO! that has the spare input ("input 8 of LOGO! 8.4"). The input is flagged as a Network Output.
• LOGO! B (target): The station that owns the free Q to drive the 5th load. It receives the Network Input from station A and uses it to drive its local Q (e.g., Q4 of LOGO! 8.1/8.2).

Either LOGO! can be the source; the choice is driven by which one has the spare input that matches the physical wiring of the 5th-load command (a pushbutton, a sensor, an enable signal from elsewhere).

4.2 Topology Diagram

5. Concrete Worked Example (the User's Confusion)

The user asked for "an example of a switch input in the first logo, input 1, and output Q4 in the second logo." That maps directly to the network I/O mechanism:

1. A physical switch is wired to I1 of LOGO! A (the LOGO! 8.4).
2. In the LOGO! A program, drag the I1 connector to the diagram, right-click it, and enable Network Output. Assign it to NQ1. The connector on the diagram now carries a small "globe" marker indicating that its state will be transmitted to the network.
3. Switch to the LOGO! B program. From the toolbox, insert a Network Input (NI) block. In the block properties, set:

   Source station : Station 1 (LOGO! 8.4)
   Source address : NQ1
   Local address  : NI1 (auto-assigned by LOGO! Soft Comfort)

4. The NI1 block now behaves like a digital input on LOGO! B. Connect its output to the Q4 coil on LOGO! B.
5. Wire the 5th physical load to terminals of Q4 on LOGO! B.

Closing the switch on I1 of LOGO! A causes LOGO! A to publish NQ1=1; the next scan of LOGO! B reads NI1=1, evaluates the program, and energises Q4 on LOGO! B. From the user's perspective, the 5th output lives on LOGO! B but is commanded by an input on LOGO! A.

6. Step-by-Step Configuration in LOGO! Soft Comfort

6.1 Set Static IP Addresses on the LOGO! Units

Static IP is mandatory for a deterministic network project. DHCP lease renewals can briefly take a station offline, which drops all NIs to their substitute value for one or two scans.

1. On each LOGO!, press ESC to enter the menu.
2. Select Network → IP Address.
3. Disable DHCP.
4. Set LOGO! 8.4 (Station A): 192.168.0.10 / mask 255.255.255.0.
5. Set LOGO! 8.1/8.2 (Station B): 192.168.0.11 / mask 255.255.255.0.
6. Confirm with OK.

6.2 Create the Network Project

1. Launch LOGO! Soft Comfort 8.4 (the higher-version editor, since it can open and edit both 8.1/8.2 and 8.4 firmware projects).
2. File → New and select the LOGO! 8.4 hardware type.
3. In the project tree, right-click Network → Add Station. Add a second station with the LOGO! 8.1/8.2 hardware.
4. Assign station numbers: A = 1, B = 2.
5. Assign IPs as configured in 6.1.
6. Save as a network project (file extension .lsc or .lscp).

6.3 Configure the Network Output on Station A

1. Open the LOGO! 8.4 program in FBD or LAD view.
2. Drag the input that commands the 5th load (the user's I8) to the diagram.
3. Right-click the connector → Properties → tick Network Output → assign NQ1.
4. Confirm. The connector now displays the NQ1 marker on the diagram.

6.4 Configure the Network Input on Station B

1. Open the LOGO! 8.1/8.2 program in the same network project.
2. From the toolbox, insert a Network Input block (globe-icon connector).
3. Properties:
   • Source station: 1 (LOGO! 8.4)
   • Source address: NQ1
   • The local NI number is auto-assigned (NI1 in this case).
4. Wire NI1's output to the coil of Q4 on LOGO! B.

6.5 Wire the 5th Load

Connect the 5th physical load to the relay contacts (or transistor output) of Q4 on LOGO! B. For a 230RCE base, Q1-Q4 are relay contacts rated per the device datasheet. For a 24RCE/TCE base, the transistor outputs switch the 24 V DC load negative; check polarity.

6.6 Compile and Download

1. Press F5 (Compile) on the network project. LOGO! Soft Comfort compiles each station's program separately and validates the network map.
2. Connect the PC to either LOGO!'s Ethernet port, or to a switch on the same subnet.
3. Use Tools → Transfer → PC → LOGO! for each station. You can also download the full network project to station A and let it forward station B's program across the Ethernet link.
4. If prompted, put the LOGO! in STOP to accept the new program, then back to RUN.

7. Verification

8. Limitations and Gotchas

• Substitute value on link loss. Each NI has a configured substitute value (default 0). If a fail-safe (energise-to-trip) output is required, add a watchdog timer in Station B that holds the output only while the NI pulses within a known interval.
• Scan coupling. The remote input must be evaluated in Station A's scan before the NI updates in Station B. For sub-10 ms events, network I/O is unsuitable; use direct wiring or a faster protocol.
• Number of NIs/NQs per project. Up to 64 NIs and 64 NQs. The 5th-output use case consumes 1 NI and 1 NQ.
• LOGO! Soft Comfort version compatibility. A 8.4 project that contains an 8.1/8.2 station must be opened in the 8.4 editor. Opening it in 8.1/8.2 will strip the higher-version features and may corrupt the network mapping.
• SD card cross-loading. Network programs are not always portable via SD card between firmware versions. Use PC-based transfer (USB or Ethernet) for network projects.
• Web server. Each LOGO! 8 has an independent web server that exposes only that station's local I/O. Network I/O is not mirrored onto the web server; you cannot read Station A's input from Station B's web page.
• Display mapping. The on-board LOGO! display and the LOGO! TD text display show the NI/NQ status. Use this for fast field diagnostics without a PC.

9. Alternatives Worth Considering

10. Field-Commissioning Checklist

1. Document the IP address, station number, and NI/NQ mapping on a paper label stuck to each LOGO!.
2. Ping test before powering the loads. A network that boots cleanly and reaches RUN with a healthy link should keep the NI alive.
3. Cycle test every output 3-5 times. Watch the LOGO! display for the NI state changing in lockstep with the source input.
4. Power cycle the network (pull the Ethernet cable, then restore). Confirm the 5th output returns to the correct state on its own.
5. Update the FBD/LAD documentation to show the NQ → NI path. Future maintainers will not infer the network coupling from a 5th output that is physically on a different station.
6. Configure the LOGO! display to show the NI status on Station B's main screen so a field tech can see at a glance whether the 5th output is "live" or "link lost".
7. Verify DHCP is disabled on both stations. Re-enable it temporarily in test mode and watch the NI flicker as the lease renews.

11. Troubleshooting Matrix

12. Glossary

• NI — Network Input. A digital input on the local station that is sourced from a remote station's NQ.
• NQ — Network Output. A digital output published from the local station for remote stations to consume.
• FS — Firmware Status. The trailing two-digit version (e.g., FS:04 = 0BA8 with firmware V1.04.x.x).
• 0BA8 — The 8th-generation LOGO! family, marketed as "LOGO! 8".
• DM8 / DM16 — Digital expansion modules, 8 or 16 points, mix of inputs and outputs.
• RCE / TCE — Relay output / Transistor output variant of the LOGO! base.

13. References to Official Documentation

• Siemens Industry Online Support — LOGO! 8 system manual, LOGO! Soft Comfort online help, application examples.
• Siemens LOGO! product page — catalog numbers, variant comparison, downloads.

FAQ