Configuring Samkoon HMI Communication with Siemens S7-1200 PLC

Samkoon HMIs integrate with the Siemens S7-1200 family through the S7 communication protocol (PUT/GET) carried over ISO-on-TCP (RFC 1006) on TCP/102. Because third-party panels rely on absolute addressing rather than the symbolic tag binding used inside a TIA Portal project, the controller side must be configured to permit PUT/GET access, and any DB that the panel must read or write must be created without the "Optimized block access" attribute. This reference walks through every step required to bring up a stable link, then maps the field-proven failure modes to corrective actions.

1. Overview of the S7 PUT/GET Communication Path

PUT/GET is the oldest, simplest S7 user-data mechanism. The HMI (or any S7 station) opens an ISO-on-TCP connection to the CPU on TCP port 102, then issues PUT (write) and GET (read) requests against a partner CPU. The active partner specifies the remote slot and either a memory area (M, I, Q) or a data-block number, byte offset, and bit offset. No program block changes are required in the S7-1200 user program; the communication runs entirely through the system firmware of the CPU.

Because the protocol predates symbolic names, it is fundamentally absolute. Samkoon's S7-1200 driver works exactly the same way: the panel builds an S7 frame addressed to e.g. DB100.DBW0 and the CPU interprets the byte address against the runtime layout of DB100. If the DB is compiled with optimized access, the byte layout no longer matches the source order in TIA Portal and the panel reads garbage or returns an access error.

2. Prerequisites and Compatibility Matrix

Before commissioning, verify the four components below match a supported combination. Mixed versions are a frequent source of intermittent "connection drop" or "object access error 0x8104" faults.

Network prerequisites:

• Both devices on the same IPv4 subnet (or routed through a managed switch without NAT).
• CPU PROFINET interface configured with a static IP (DHCP disabled).
• No firewall on the engineering PC or panel blocking TCP/102 outbound to the CPU.
• Maximum of 8 simultaneous S7 PUT/GET connections per S7-1200 CPU. This is a hard firmware limit, not a project setting.

3. Network Topology and Addressing

A typical point-to-point deployment looks like the following. For multi-panel projects, place the CPU and all HMIs on the same PROFINET subnet so that the S7 connections are terminated directly by the CPU's integrated interface.

Note the rack/slot pair: the S7-1200 always lives at Rack 0 / Slot 1 for the integrated PROFINET interface. If you are connecting through a CP 1243 module instead of the onboard interface, change slot to the CP's slot in TIA Portal hardware catalog (commonly slot 2 or 3).

4. Enabling PUT/GET in TIA Portal

1. Open the S7-1200 project in TIA Portal.
2. Select the CPU device in the project tree and double-click Device configuration.
3. In the device view, click on the CPU module (not the PROFINET port).
4. Open the Properties pane → Protection & Security.
5. Scroll to the Connection mechanisms section.
6. Tick Permit access with PUT/GET communication from remote partner.
7. Compile the hardware (right-click CPU → Compile → Hardware and software only) and download to the CPU.

5. Configuring Data Blocks for Absolute Access

Each DB the Samkoon panel must touch must be created or modified with the Optimized block access attribute disabled. Without this, the absolute byte offsets compiled into the panel project will not match the CPU's runtime layout.

1. Right-click the data block (e.g. DB100) in the project tree.
2. Choose Properties.
3. Open Attributes.
4. Clear the checkbox Optimized block access.
5. Confirm with OK.
6. Recompile the software and download only the affected DB.

Once optimized access is off, the panel can address data using the standard S7 syntax:

6. Samkoon HMI Project Configuration

The Samkoon configuration software (SKWorkshop) treats the S7-1200 as a polled client. Configure the connection once at project level; every tag you create inherits the same transport.

1. Open SKWorkshop, create or open the project.
2. Open System Settings → Device and select the correct Samkoon panel model.
3. Open System Settings → Communication → New Link (or PLC Link in older builds).
4. Choose driver: Siemens S7-1200 (Ethernet). If only a generic S7-200/300/400 driver is offered in your build, select that — the wire format is identical.
5. Set the parameters:

Save and download the project to the panel. The panel immediately attempts to open the ISO-on-TCP connection; check the panel's system diagnostic screen for a green connection indicator before continuing.

7. Tag Definition and Polling Strategy

Tag definitions in SKWorkshop bind a name (used inside the panel screens) to a CPU address. Always declare a unique memory area + offset pair; the panel does not validate the address against the CPU's symbol table, so duplicates silently overwrite each other.

Recommended tag layout for a small machine:

Optimization rules:

• Group tags that change together into a contiguous block (e.g. all alarms in one word) so the panel can fetch them in a single PUT/GET request.
• Reserve the lowest M-bit range (M0.0–M15.7) for HMI handshaking only; do not use it for logic that the CPU program also evaluates heavily, because every panel poll forces a memory write commit.
• Use MW0 only for short status words, never for retentive counters; the panel may re-write the area on reconnect.

8. Retentive Bit Memory Considerations

Bit memory M in the S7-1200 can be declared retentive in TIA Portal under PLC → Properties → Retentive memory. The default retentive range starts at MB0. This has two practical consequences for third-party panels:

1. If the HMI writes to a retentive MB and the CPU is power-cycled, the value survives. Use this for setpoints that should persist across reboots.
2. If the HMI writes to a retentive bit during commissioning and the CPU is later reset to factory defaults, the retentive bits keep the last HMI value. Always perform a "Reset to factory" of the CPU before re-commissioning to clear stuck HMI state.

9. Verification Procedure

After configuration, walk through these checks before declaring the link commissioned.

1. Connection indicator: Samkoon system screen should show "Connected" or "Online" with no red fault icon.
2. CPU side diagnostic buffer: In TIA Portal, go to Online & diagnostics → Diagnostic buffer. There should be no entry of class "Communication error" with text PUT/GET access denied.
3. Tag round-trip test: Force DB100.DBX0.0 to TRUE in the CPU using a watch table. The bound Samkoon button should show the "pressed" state within one poll cycle (default 500 ms).
4. Write from panel: Toggle DB100.DBX0.1 to TRUE from the panel. Watch table should show the value change within one poll cycle.
5. Diagnostic counters: In the CPU's Online & diagnostics → Communication, verify the S7 connection state shows ESTABLISHED and no CONN_REFUSED events since startup.
6. Load test: Add 50 tags and reduce poll interval to 200 ms. Watch the CPU's communication load — should remain under 30% to leave headroom for PROFINET.

10. Troubleshooting Matrix

11. Performance and Limits

The S7-1200 dedicates a portion of its cycle time to communication. The following limits are firm:

• 8 active S7 PUT/GET connections maximum, regardless of project configuration.
• 240-byte maximum user-data payload per PUT request; 240 bytes per GET response.
• Communication load: keep below 50% of cycle time to avoid cycle-time overrun faults.
• For installations exceeding 500 tags polled at <500 ms intervals, move to a 1500 CPU or split the panel population across two CPUs.

If the panel-side poll timer is shorter than the CPU's actual update time, the panel will queue requests and visually lag. Increase the poll interval in SKWorkshop until the lag disappears, then back off by 20% for stability.

12. Diagnostic Tools and References

Official Siemens documentation paths to confirm the steps above:

• S7-1200 Programmable Controller — System Manual — primary hardware and protection-level reference.
• Communication with S7-1200 / S7-1500 — function-block and protocol reference for PUT/GET.
• TIA Portal Help: Protection & Security — description of the connection-mechanisms toggle.
• S7-1200 CPU 1215C DC/DC/DC Operating Instructions — sample hardware manual with rack/slot information.
• Communication functions of the S7-1200 — port assignments and connection limits.