Connecting Two LOGO! 8 PLCs to a KTP600 Basic Mono PN HMI

1. Problem Definition and Scope

Many compact machine designs replace a single larger controller with two or more LOGO! 8 units (Siemens order-number family 6ED1052-...) cooperating over their built-in Ethernet port, while a single low-cost KTP600 Basic mono PN (6AV6647-0AB11-3AX0) serves as the operator panel. The challenge is that the HMI must establish two independent S7 connections on one Ethernet cable, one per LOGO!, while the LOGO! 8 firmware has a hard ceiling on the number of simultaneous S7 communication partners it will accept.

This reference documents the engineering required to:

• Plan IP addresses and subnet topology for 1 HMI + 2 LOGO!.
• Configure the LOGO! 8 Ethernet parameters using LOGO! Soft Comfort.
• Build the project in TIA Portal V18 with the LOGO! HSP installed.
• Create two S7 connections on the KTP600 and map tags to the right LOGO!.
• Verify the system and recover from the most common commissioning faults.

2. Prerequisites

3. Network Topology and IP Plan

The three devices share one subnet. The following address plan is used throughout the rest of this article:

Each LOGO! 8 provides a fixed S7 slot for its server connection. LOGO! Soft Comfort exposes this as a TSAP; the slot is appended to the IP address when configuring TIA Portal. The two LOGO! units must therefore use different slot numbers (slot 1 and slot 2 in the example) so that the HMI can route S7 PDUs to the correct partner.

4. Configuring LOGO! 8 Ethernet Parameters

On the LOGO! itself, navigate the integrated HMI (or use LOGO! Soft Comfort > Tools > Ethernet Connections) and set:

1. IP address: 192.168.10.11 (unit #1) / 192.168.10.12 (unit #2).
2. Subnet mask: 255.255.255.0.
3. Gateway: 0.0.0.0 (leave blank if no router present).
4. Allow S7 communication: Enabled (LOGO! 8.2 and newer).
5. S7 connection slot: 1 for unit #1, 2 for unit #2.

From LOGO! Soft Comfort V8.4 onward, you can also verify the open TCP port (102/TCP) with the integrated diagnostic. The maximum number of simultaneous S7 partners is firmware-dependent:

5. Building the TIA Portal Project

1. Open TIA Portal V18, choose Create new project.
2. Install the LOGO! 8.4 HSP from Options > Support Packages if the LOGO! devices do not appear in the device catalog.
3. Add the first LOGO! with Add new device > Controllers > LOGO! > LOGO! 8 > 6ED1052-1xxx08-.... Repeat for the second LOGO!.
4. Add the HMI: Add new device > HMI > SIMATIC Basic Panels > 6" > KTP600 Basic mono PN (6AV6647-0AB11-3AX0).
5. Open Devices & Networks and connect each LOGO! Ethernet port to the HMI PROFINET port using the Connections editor. TIA Portal automatically proposes one S7 connection per link.

The result is a project tree containing three devices. The HMI node now lists two connections: HMI_Connection_1 and HMI_Connection_2.

6. Configuring the Two S7 Channels on the KTP600

For each connection, verify the following parameters in HMI_Connection_x > Properties > General:

Two additional area pointers must be enabled under Properties > Area pointers:

• Coordination (one byte, used by KTP600 for life-bit).
• Date/time (only needed if you want the HMI to write the time to both LOGO! clocks; both connections can use the same PG pointer).

7. Tag Mapping to the LOGO! VM Area

The LOGO! 8 exposes its variables through the Variable Memory (VM) mapping. In TIA Portal, when you select a tag of type Word, address VW0 on a LOGO!, the driver requests the VM area of that particular LOGO! via the matching connection. No manual mapping of tags to LOGO! addresses is required beyond declaring the address range you want to read.

Reference ranges (LOGO! 8.3 / 8.4):

To display a digital input of LOGO! #2 on the HMI, create a tag in the HMI tags editor, select connection LOGO_B and address V0.0. To display the same physical point on LOGO! #1, address V0.0 on connection LOGO_A. The connection field is what selects the partner, not the address.

8. Building HMI Screens

1. Open HMI > Screens > Add new screen. Create at minimum Overview, Machine A, Machine B, and Alarms.
2. On the Overview screen, place two Status/Force views or two Symbolic IO fields showing a tag from each LOGO! so the operator can confirm both connections are live at a glance.
3. Use the Connection status system function on screen change events to log which partner is currently unreachable.
4. For shared setpoints (e.g. global production counter), write to both VM areas using two separate tags triggered from the same button.

Sample tag list excerpt:

HMI_Tag_Block "LogoA_DI0"     : BOOL, conn=LOGO_A, addr=V4000.0
HMI_Tag_Block "LogoA_Run"     : BOOL, conn=LOGO_A, addr=V6000.0
HMI_Tag_Block "LogoA_Cnt_SP"  : INT,  conn=LOGO_A, addr=VW200
HMI_Tag_Block "LogoB_DI0"     : BOOL, conn=LOGO_B, addr=V4000.0
HMI_Tag_Block "LogoB_Run"     : BOOL, conn=LOGO_B, addr=V6000.0
HMI_Tag_Block "LogoB_Cnt_SP"  : INT,  conn=LOGO_B, addr=VW200

9. Verification and Commissioning

1. Compile the project (TIA Portal > HMI > Compile > Software (rebuild all)). Errors here usually indicate an address outside the VM range or a typo in the connection name.
2. Download to the KTP600 via Ethernet. Confirm transfer mode PN/IE and target IP 192.168.10.50.
3. Start Runtime on the panel. The "Connection status" indicator should turn green for both LOGO_A and LOGO_B within 2–5 seconds.
4. Force a value on each connection from TIA Portal (HMI Tags > right-click > Modify) and confirm the LOGO! 8 reacts. If the LOGO! is running a Soft Comfort program that uses a network input (NI), write to that NI's VM location.
5. Cycle audit: monitor LOGO_A.Cnt_SP on the panel and verify it updates inside the configured 500 ms cycle. Slower updates indicate network collision or switch mis-configuration.

10. Troubleshooting Matrix

11. Limits, Cycle Times and Performance Notes

Two parallel S7 connections share the 100 Mbit/s link. The effective update rate on the panel is determined by the slowest of:

• LOGO! program cycle time (typical 10–50 ms depending on program length).
• HMI configured cycle (minimum 100 ms; 500 ms is a safe default).
• TCP keep-alive handled by the LOGO! (default 30 s).

With a 500 ms HMI cycle and ten tags per connection, the load on the network is < 1 % and is dominated by the LOGO! cycle, not by the panel. If you notice latency, first reduce the number of acquired tags, then shorten the LOGO! cycle by removing unused blocks in the Soft Comfort program.

For diagnostics over the same network, enable the KTP600's Diagnostics screen from the project settings. It shows live connection status, partner IP and last error code without requiring additional area pointers.

12. Field-Proven Commissioning Checklist

• Reserve one IP per device; document the plan in the cabinet drawing.
• Set unique LOGO! slot numbers (1 and 2 minimum).
• Disable web server / FTP on the LOGO! if not used to free TCP sockets.
• Stick a label with IP and slot on each LOGO! so service engineers do not have to reconfigure.
• Export the TIA project and the LOGO! Soft Comfort program to the same archive folder after every change; a missing LOGO! program is the most common cause of "everything compiles but nothing works" in the field.