S7-1200 TCP Port 49999 Configuration Beyond the 49151 UI Limit

Problem: S7-1200 Cannot Reach a TCP Server on Port 49999

When configuring an S7-1200 CPU to communicate with a third-party TCP device that listens on a fixed, non-standard port (for example a marquee display or status sign bound to port 49999), engineers hit a hard stop inside the TIA Portal configuration UI. The TCP connection dialog of TSEND_C, TRCV_C, and the TCON wizard validates the Local Port and Remote Port fields against a maximum of 49151. The dialog refuses any value greater than 49151 and the project will not compile while the value is out of range. The third-party device port cannot be changed on the field device side, so the controller must adapt.

Root Cause: Input Validation in the Connection Parameter UI

The 49151 ceiling is a TIA Portal front-end input check, not a CPU firmware limit. The underlying S7-1200 PROFINET/Industrial Ethernet stack supports the full TCP/UDP port range 1-65535 on the open user communication instructions (TCON, TSEND, TRCV, TUSEND, TURCV). The wizard exposes only the "registered" port band (1-49151) as selectable because the dynamic/private range is normally assigned by the OS to outbound sockets.

Because the dialog writes the port directly into the connection DB (data block of type TCON_Param), bypassing the dialog and editing the DB yourself unlocks the full range. Once the DB is compiled with a value > 49151, the CPU opens the socket on that exact port without complaint.

Affected Products and Firmware Versions

Reference: Communication protocols and ports used by Ethernet communication (Siemens SIMATIC S7-1200 Manual Collection, English).

Architecture: How TCON Allocates a Socket on the S7-1200

Every TCP connection on the S7-1200 is described by an instance DB of PLC data type TCON_Param (system UDT). The CPU uses this DB to allocate the socket via the internal PROFINET stack when TCON.REQ is triggered. The RemotePort and LocalPort fields are UINT (16-bit unsigned, 0-65535). Writing a value of 49999 (0xC34F) into either field is fully legal at the data type level - the restriction exists only in the HMI input mask that normally edits those fields.

Solution 1: Edit the TCON_Param Connection DB Directly

The cleanest method is to keep the standard TIA Portal connection wizard (so PROFINET diagnostics still recognize the connection) and only edit the raw byte values inside the generated instance DB.

1. Insert a new TSEND_C or TRCV_C block in the program. In the configuration dialog, set Connection type = TCP, Active connection establishment = TRUE (S7-1200 initiates), and enter Remote Port = 49999 and Local Port = 0 (auto-assign) or any free port below 49151 for the initial compile.
2. Click Generate to create the instance DB. Note the DB name (for example InstTSEND_C_DB).
3. Open the generated DB, switch the view to All, and locate the static variable of type TCON_Param (typically named TCON_Param_1 or visible as the id, ConnectionType... structure starting at offset 0).
4. Modify the port fields. For RemotePort (offset 39/40), enter 0xC3 at offset 39 and 0x4F at offset 40. For LocalPort (offset 56/57), enter 0xC3 / 0x4F to bind locally to 49999, or 0x00 / 0x00 to let the OS pick.
5. Disable the watch tables for these bytes if needed - TIA Portal sometimes resets byte values to zero on re-edit. Lock the values with ATTR = "Read-only in HMI" or write them at runtime via a MOVE block (see Solution 2).
6. Compile. TIA Portal will emit a non-fatal warning ("Port number outside the permissible range") but the project builds successfully because the type check on UINT accepts the value.
7. Download to the CPU. Trigger TCON.REQ. The CPU opens the TCP socket on port 49999 and the marquee responds.

Solution 2: Runtime Override with a MOVE Block

If the engineer is not comfortable editing raw DB bytes, or if TIA Portal refuses the offline value at compile time on certain versions, force the port at runtime by copying a constant into the TCON DB before each TCON call.

Ladder logic - FB boundary:

Network 1 - Force remote port before TCON
      "InstTSEND_C".TCON_Param_1.RemTsapId[1]  :=  16#C3;   // high byte
      "InstTSEND_C".TCON_Param_1.RemTsapId[2]  :=  16#4F;   // low byte
      "InstTSEND_C".TCON_Param_1.RemTsapIdLen :=  B#16#2;

Network 2 - Trigger connection
      "Tag_TCON_REQ"  :=  TRUE;             // set for one scan via edge
      "InstTSEND_C".REQ   :=  "Tag_TCON_REQ";

SCL equivalent:

// Patch port 49999 (0xC34F) into the TCON DB before requesting the connection
"InstTSEND_C".TCON_Param_1.RemTsapId[1] := 16#C3;
"InstTSEND_C".TCON_Param_1.RemTsapId[2] := 16#4F;
"InstTSEND_C".TCON_Param_1.RemTsapIdLen := 2;
IF "FirstScan" THEN
  "InstTSEND_C".REQ := TRUE;
END_IF;

Place the MOVE (or direct byte assignment in SCL) immediately before TCON in every OB1 cycle. The byte write happens before the CPU reads the connection description, so the socket is always opened on the patched port.

Solution 3: Manual TCON/TSEND/TRCV Split (No Wizard)

Engineers who want full control - or whose TIA Portal version refuses to compile any port above 49151 even as a DB value - can drop TSEND_C/TRCV_C entirely and call the legacy instructions directly.

Steps:

1. Create a new global DB DB_Marquee with one variable of PLC data type TCON_Param named connParams. This bypasses the wizard entirely - no UI range check.
2. Set BlockLength = 64, Id = 1, ConnectionType = 16#0B, ActiveEstablished = TRUE, LocalDeviceId = 1 (PROFINET interface), RemStaddrLen = 4.
3. Fill RemStaddr[1..4] with the marquee IP (for example 192.168.0.50 becomes 192, 168, 0, 50).
4. Fill RemTsapId: byte 1 = 16#C3, byte 2 = 16#4F (port 49999 big-endian). RemTsapIdLen = 2.
5. Fill NextStaddr for the local port if you need a fixed source port: byte 1 = 16#C3, byte 2 = 16#4F. NextStaddrLen = 2. Use 0/0 to let the OS auto-assign.
6. Call TCON(REQ := startPulse, ID := 1, CONNECT := "DB_Marquee".connParams).
7. Once DONE = TRUE, send data via TSEND; receive via TRCV with ADHOC = TRUE for variable-length marquee responses.

Verification Procedure

1. Open Online & Diagnostics on the S7-1200, navigate to Diagnostics > ProDiag / Connection overview or use a watch table on the TCON instance. Confirm DONE = TRUE and ERROR = FALSE / STATUS = 16#0000.
2. From a Windows PC on the same subnet, run netstat -an | findstr 49999. The S7-1200 IP should appear with ESTABLISHED against port 49999 on the marquee IP. A SYN_SENT or CLOSE_WAIT state indicates the CPU opened the socket but the marquee never accepted - check firewall, IP, and that the device is in server mode.
3. Send a known marquee payload (ASCII text or vendor protocol frame) via TSEND. Use a tap like Wireshark with port filter tcp.port == 49999 to confirm the bytes leave the CPU and the device acknowledges.
4. Check STATUS after TSEND: 16#7000 = busy, 16#7002 = done, 16#8085 / 16#80A1 = connection fault. See the S7-1200 system manual, section "Status codes of TSEND/TRCV" for the full table.
5. Use the marquee vendor's test utility (often a Windows TCP client) and point it at the S7-1200 IP on port 49999. If the CPU is the server side (ActiveEstablished = FALSE), the utility should see the listening socket immediately.

Troubleshooting Matrix

Design Considerations and Constraints

• Connection count: The S7-1200 PROFINET interface supports up to 8 open user communication connections simultaneously. Each TSEND_C/TRCV_C consumes one. Above 8, the CPU returns STATUS 16#80C3.
• Firmware floor: Open user communication has been available since the first S7-1200 firmware. TCON/TSEND/TRCV were extended with ADHOC receive and UDP variants in V4.0; the G2 generation (V5.0+) does not change the instruction semantics.
• Watch out for collations: If the project also uses OPC UA on the CPU, mind the local port - OPC UA server default is 4840. Keep TCON local ports distinct from system services.
• Security: Disabling the port ceiling in TIA Portal does not disable any runtime firewall. The S7-1200 CPU (V4.4+) supports a built-in firewall with connection rules; add a rule permitting remote IP/port 49999 if security is enabled.
• Determinism: TCP retransmits and the marquee's server-side response time are non-deterministic. For sub-100 ms control loops, consider UDP (TUSEND/TURCV, ConnectionType = 16#13) on the same port range instead of TCP.
• Diagnostic visibility: ProDiag in TIA Portal V17+ can supervise TCON/TSEND/TRCV status changes natively. Add a ProDiag FB to surface ERROR transitions in the HMI.

When to Use Which Instruction

Related Configuration: PROFINET Interface Diagnostics

If the marquee also exposes a web UI on another port (80, 443, 8080), use the CPU's Online & Diagnostics > PROFINET interface > Port statistics view to verify the physical link and check for CRC errors that would silently drop TCP segments. The official SIMATIC S7-1200 System Manual describes how to enable the Web server (default port 80) for diagnostics: S7-1200 Manual Collection - Communication.