Configuring SMS over IP on S7-1200 CPU 1212 with M875 Telecontrol

Configuring SMS over IP on S7-1200 CPU 1212 with the M875 Telecontrol Component in TIA Portal

Engineers integrating an S7-1200 CPU 1212 into a remote-monitoring application frequently need an SMS-over-IP path that works when the public Internet is reachable but the plant LAN is not. The reference architecture pairs a Siemens S7-1200 station with the M875 telecontrol component (commonly implemented with the SCALANCE M875 industrial mobile router) and a Telecontrol Server Basic (TCSB) instance that forwards alarms via an SMPP-capable SMS gateway. This article consolidates the configuration, programming, and verification steps required to make that path operational in TIA Portal, with concrete block interfaces, sample SCL code, parameter tables, and a troubleshooting matrix.

1. SMS-over-IP Architecture Overview

The end-to-end path is short, but each hop has its own parameters and failure modes:

Key hop characteristics:

Two architectural decisions drive the rest of the configuration:

1. Direct SMS via CSD/GSM — older method, the CP 1242-7 sends SMS directly to an SMSC over a CSD data call. Obsolete in most regions because 2G CSD is being decommissioned; not recommended for new deployments.
2. SMS via TCSB and SMPP gateway (recommended) — the CP 1242-7 establishes a permanent or on-demand GPRS/LTE tunnel to Telecontrol Server Basic, and TCSB forwards the message via SMPP to a commercial SMS gateway. This is the path covered here.

2. Hardware Prerequisites and Component Selection

Verify every item before commissioning. A missing firmware update is the most common cause of "TCS cannot establish connection" faults on otherwise correct projects.

3. Network Topology and IP Planning

The address plan must accommodate three segments without overlap:

Configure the M875 as the default gateway for the CP 1242-7. In the CP 1242-7 properties under "Ethernet interface > IP protocol > Router", enter 192.168.1.1 as the default router and the carrier-supplied DNS servers. If you use the CP 1243-7 LTE as an alternative to the M875, the CP itself acts as the mobile interface and the routing entry becomes 0.0.0.0 0.0.0.0 <CP-as-router-IP>.

4. SCALANCE M875 Industrial Router Configuration

Access the Web Based Management (WBM) at https://192.168.1.1. Default credentials are on the device label; change them on first login.

4.1 Mobile interface

1. Interfaces > Mobile: set APN, Username, and Password as supplied by the M2M carrier.
2. Disable PIN if the SIM is provisioned without one (most industrial M2M SIMs are).
3. Set Connection mode to "Permanent connection" so the TCSB tunnel stays established; this reduces SMS latency from tens of seconds to under two.
4. Enable Data roaming only if cross-border operation is required.

4.2 Firewall rules

4.3 VPN (optional, recommended for sensitive sites)

For an IPsec tunnel back to the corporate control center, define the remote subnet (10.0.0.0/24) as a phase-2 selector. The CP 1242-7 will then route TCS-bound traffic through the encrypted tunnel without further changes on the CPU side. Refer to the SCALANCE M875 operating instructions in the SIMATIC NET manual collection for the IPsec parameter set.

5. TIA Portal Project Setup for S7-1200

1. Create a new project in TIA Portal V17 or higher; choose "Add new device > SIMATIC S7-1200 > CPU 1212" matching the article number suffix (DC/DC/DC vs DC/DC/RLY).
2. Set the CPU's IP address to 192.168.0.1/24; subnet mask 255.255.255.0; router 192.168.0.1 (no router on the CPU itself).
3. In the device catalog, locate "Communication > CP 1242-7" (article 6GK7242-7KX30-0XE0). Drag it into the same S7-1200 station; TIA Portal auto-assigns slot 1 next to the CPU.
4. Configure the CP IP address to 192.168.0.2/24 and the default router to the M875 LAN address 192.168.1.1.
5. Insert the Telecontrol interface of the CP and choose "Telecontrol Server Basic" as the connection target.

5.1 Telecontrol configuration in the CP properties

6. Telecontrol Server Basic Installation and SMS Configuration

Refer to the entry Communication between RTUs with S7-1200 and Telecontrol Server Basic for the canonical installation sequence. Key points for SMS use:

1. Install TCSB on a dedicated Windows Server. Activate the "Alarm-SMS via SMPP" option during setup.
2. Import the station setup file exported from TIA Portal (.tcs). The wizard maps the CP's station number to the TCSB station and ingests the authentication key automatically.
3. Open TCSB Configuration > SMS Gateway and enter:

4. Test the SMPP bind via the "Test connection" button. A success log entry confirms the SMS path is operational before any PLC code is written.
5. Define at least one SMS recipient list and bind it to the station so that triggered alarms reach the right phone numbers.

7. S7-1200 SMS Program: Library Integration

The S7-1200 telecontrol library is shipped with TIA Portal under Libraries > Global Libraries > Telecontrol. It contains the FBs and DBs required to send messages. Reference it explicitly in the project to avoid copy-paste errors.

7.1 Library overview

7.2 Add the library

1. In TIA Portal: Options > Global libraries > Open library > "Telecontrol_S7_1200".
2. Drag TC_SMS and TC_CONFIG into the project "Program blocks" folder.
3. Open the "Telecontrol interface" of the CP 1242-7, switch to the "Message configuration" tab, and enable the events that should generate an SMS (binary tags, analog thresholds, acknowledgement messages).

7.3 SCL sample: SMS sender wrapper

The following SCL FB wraps TC_SMS with a one-shot trigger, status decoding, and a debounce on success so the same alarm cannot generate duplicate messages within a 60-second window.

FUNCTION_BLOCK "FB_SMS_Alarm"
{ S7_Optimized_Access := 'TRUE' }
VERSION : 0.1
VAR
    TC_SMS_Inst : TC_SMS;
    iTC_DB : TC_DB;
    bTrigger : BOOL;
    sPhone   : STRING[20];   // international format, e.g. "+4917xxxxxxxx"
    sText    : STRING[160];  // GSM 7-bit: 160 chars; UCS-2: 70 chars
    bEdge    : BOOL;         // rising-edge memory
    tonDebounce : TON;       // 60 s lockout after a successful send
    rtEdge    : R_TRIG;
END_VAR
BEGIN
    rtEdge(CLK := bTrigger, Q => bEdge);
    tonDebounce(IN := TC_SMS_Inst.DONE, PT := T#60s);

    IF bEdge AND NOT tonDebounce.Q THEN
        TC_SMS_Inst.REQ   := TRUE;
        TC_SMS_Inst.ID    := 1;
        TC_SMS_Inst.PHONE := sPhone;
        TC_SMS_Inst.TEXT  := sText;
    ELSE
        TC_SMS_Inst.REQ   := FALSE;
    END_IF;

    TC_SMS_Inst(
        REQ    := TC_SMS_Inst.REQ,
        ID     := TC_SMS_Inst.ID,
        PHONE  := TC_SMS_Inst.PHONE,
        TEXT   := TC_SMS_Inst.TEXT,
        DONE   => TC_SMS_Inst.DONE,
        BUSY   => TC_SMS_Inst.BUSY,
        ERROR  => TC_SMS_Inst.ERROR,
        STATUS => TC_SMS_Inst.STATUS);
END_FUNCTION_BLOCK

Call the wrapper from an alarm OB (e.g. OB82 or a cyclic OB with edge detection on the process tag) and route the STATUS word into the HMI diagnostic screen.

7.4 TC_SMS STATUS word decoding

8. SMS Trigger Logic and Acknowledgment

Trigger the SMS from event-driven OBs to keep scan-time impact minimal:

• OB82 (diagnostic interrupt) — module fault, SM 1231 wire break, CP 1242-7 signal loss.
• OB1 (cyclic, edge detected) — process alarms such as tank level > high-high or motor overload.
• Time-of-day — daily status report at 07:00 local time using OB10.

For two-way acknowledgment, configure TC_RECV to accept a designated SMS keyword ("ACK") from any authorized number. Map TC_RECV.TEXT into a string compare block and set the corresponding process tag to acknowledge the alarm.

9. Verification and Diagnostics

1. CP online diagnostics. In TIA Portal, mark the CP 1242-7, choose "Online & diagnostics", then "Telecontrol". Confirm "Connection state: Connected" and the active TCP socket to the TCSB public IP on port 2777.
2. TCSB station status. Open TCSB Configuration > Stations. The station should show green "connected" with the last message timestamp recent.
3. SMPP test send. From TCSB Configuration > SMS Gateway, click "Send test SMS". A delivered message confirms the operator path independently of the PLC.
4. End-to-end PLC test. Set a breakpoint at the bTrigger input of FB_SMS_Alarm and force TRUE for one cycle. Observe DONE=TRUE and the STATUS word. The phone receives the message within 2–10 s for a permanent connection.
5. HMI alarm log. Confirm the alarm appears in the WinCC Unified or Comfort Panel alarm view with the SMS status mapped.

10. Troubleshooting Matrix

11. Security, Firewall, and Mobile Operator Settings

• TLS 1.2 minimum. Force TLS 1.2 on the CP 1242-7 to match TCSB V3.4+. TLS 1.0/1.1 are deprecated and rejected by many SMSC gateways.
• Private APN. Use a private APN with carrier-side IP filtering whenever possible to deny public Internet access from the SIM.
• Source TON/NPI. Use TON=1 (international) and NPI=1 (E.164) unless your SMPP provider explicitly requires alphanumeric originator.
• SMS length. Concat SMS (>160 chars) is supported via SMPP UDH but requires provider enablement; expect per-segment billing.
• Audit trail. Enable TCSB audit logging and forward the log to a central SIEM; the "submit_sm_resp" line per message is sufficient for compliance review.

12. Performance, Limits, and Best Practices

For deeper background on the telecontrol CPs and their S7-1200 integration, see the Telecontrol CPs overview in the SIMATIC S7-1200 manual collection, and the SMS-specific sample program documented in Siemens support entry 58638283.