CP 1242-7 GPRS V2: S7-1200 LED Diagnostics and TCSB Setup

Overview

The CP 1242-7 GPRS V2 (Siemens article number 6GK7242-7KX31-0XE0) is a communications processor that connects a SIMATIC S7-1200 PLC to a GSM/GPRS mobile wireless network. It is installed on the left side of the S7-1200 CPU, is supplied from the backplane bus, and performs all wireless link management independently of the CPU cycle. A typical architecture pairs the CP with a TeleControl Server Basic (TCSB) running on a host PC, which acts as the OPC/Modbus gateway between the S7-1200 and the SCADA layer (WinCC, WinCC Flexible, or a third-party HMI).

This reference consolidates the field-experience commissioning flow into a single document. It covers LED-state interpretation, APN configuration, TCSB project setup, teleservice activation, WinCC Flexible tag exchange over GPRS, and the recurring "NETWORK LED on for 10 seconds, then off" failure mode after a STEP 7 project download.

CP 1242-7 GPRS V2 Hardware Facts

LED State Matrix and Meaning

Every commissioning hour spent on the CP 1242-7 starts at the LED panel. The five LEDs each have a precise, deterministic state, and the combination tells you exactly where in the connection stack the link has stopped.

The "DIAG blinks green, SIGNAL QUALITY green, NETWORK off" pattern that triggers this article is the canonical "logged into GSM but stuck before GPRS attach" state. The CP is physically on the cellular network but the SIM's GPRS data subscription has not been negotiated, almost always because of an APN mistake.

APN Configuration in STEP 7 (TIA Portal)

1. Open the TIA Portal project that contains the S7-1200 station.
2. In the project tree, double-click Devices & networks > CP 1242-7 V2.
3. Switch to Properties > Mobile wireless interface.
4. Enter the four APN fields exactly as the MNO (mobile network operator) published them:
   • APN name — for example internet, web.vodafone.de, or a private M2M APN.
   • APN user name — frequently empty for consumer APNs.
   • APN password — frequently empty for consumer APNs.
   • Dial-up number — *99***1# for GPRS, *99# for many European MNOs.
5. Tick Use permanent connection only if a static IP is allocated by the APN; otherwise leave unchecked so the CP can re-establish after dropout.
6. Compile and download the device configuration to the S7-1200.

Commissioning the TeleControl Server Basic (TCSB)

TCSB is the application that terminates the GPRS tunnel, holds the S7-1200 partner definition, and exposes the S7 tags as OPC DA / Modbus TCP items. The configuration step-by-step in the official Siemens application example (entry ID 39863979) is the reference workflow. The condensed form:

1. Install TeleControl Server Basic on the host PC. The install adds a Windows service Siemens.Tcsb.Server and the configuration tool TCSB Config.
2. Add a new project in TCSB Config. Define a partner for each S7-1200 station. The partner entry maps the CP's IMSI/MSISDN to an internal partner number.
3. Create a connection from the SCADA layer to TCSB (OPC DA on localhost:48020, or Modbus TCP on port 502). TCSB acts as the data concentrator; no S7-1200 IP address needs to be reachable from the SCADA network.
4. Bind the STEP 7 project to the TCSB partner by uploading the partner's TeleControl DB generated by STEP 7 (DB "TC_DB" by default) into TCSB Config under Import S7 configuration.
5. Activate the project. The TCSB service writes Started into its log; from this moment the CP is expected to dial in.

Teleservice Activation

The teleservice channel allows STEP 7 (TIA Portal) to perform an online download or online diagnostics on the S7-1200 over the same GPRS link. To enable it:

1. In TIA Portal, mark the CP 1242-7 V2 and open Properties > Teleservice.
2. Set Active = true and assign a PG/PC router (the TCSB host, reachable as the CP's telecontrol partner).
3. Choose the same TCSB partner as for runtime data.
4. In the PG/PC, configure an S7-Online route: Type = Teleservice, Partner number = CP's MSISDN.
5. From TIA Portal, choose Online > Accessible nodes; the S7-1200 should appear behind the TCSB route.

If only the runtime data path (SCADA tags) works but teleservice fails, the most common cause is the teleservice partner not being linked to the same TCSB project; verify the project name in TIA Portal matches the active project on the TCSB host.

WinCC Flexible SP3 Integration over GPRS

To make a WinCC Flexible runtime exchange tags with the S7-1200 across the GPRS link, point the HMI project at TCSB as if it were a normal S7-1200 partner:

1. In WinCC Flexible, add a new connection in the HMI tags editor.
2. Select SIMATIC S7 1200 as the PLC type, and TCP/IP as the protocol (used for OPC bridging through TCSB).
3. Set the HMI's PG/PC interface to S7ONLINE > TeleService or to an OPC DA bridge that reads from TCSB. In practice, point the connection at the TCSB host IP and use the OPC DA connection type with the local OPC server on the HMI PC.
4. Create HMI tags bound to the OPC items that TCSB exposes from the S7-1200 (e.g. S7:[TCSB_Partner1]DB100.DBW0).
5. Run WinCC Flexible Runtime with the project. Tags update at the polling interval configured in TCSB (default 1 s, but rate-limited by GPRS latency).

Root Cause of "NETWORK LED On 10 s, Then Off After Download"

Several engineers report that after a STEP 7 project download, the NETWORK LED of the CP 1242-7 turns on for roughly ten seconds, then switches off permanently even though APN, IMSI, and signal are correct. The mechanism is the following:

1. The download pushes a new configuration into the CP, which restarts its internal GSM stack.
2. The CP negotiates a PDP context, and a transient NETWORK LED on confirms the GPRS attach is successful.
3. The CP attempts the first TeleControl handshake with TCSB. If TCSB rejects the partner (wrong partner number, mismatch in the TC_DB import, or the TCSB service is stopped), the CP tears down the PDP context and switches NETWORK off.
4. The CP then waits for the next keepalive/cyclic dial retry (default 60 s) before trying again. If the partner mismatch persists, the same 10-second pattern repeats indefinitely.

Diagnostic verification: open Web diagnostics of the CP (browser on the S7-1200's engineering IP) and look for Telecontrol > Connection state > Reason for last disconnect. A 0x8000 0000-class error means authentication rejected by TCSB; a 0x80xx xxxx partner-not-found error means the partner number imported into TCSB does not match the one configured in TIA Portal.

Troubleshooting Matrix

Verification Procedure After Configuration

1. LED walk: Confirm DIAG steady green, SIGNAL QUALITY steady green, NETWORK steady green, CONNECT steady green.
2. Web diagnostics: Open http://<S7-1200 IP>/<port> and verify Connection state = Connected and Bytes sent/received > 0.
3. TCSB event log: Confirm the partner appears as Online and the timestamp of last frame is current.
4. Tag roundtrip: Force a value from STEP 7 (VAT table) and read it back in TCSB OPC test client; then flip the same tag from WinCC Flexible and confirm the value in the S7-1200's VAT.
5. 24-hour burn-in: Monitor the Last disconnect reason counter; it must stay at 0x0000 0000 for the run-in period.

Common Field-Proven Caveats

• Some MNOs (notably in North America) deactivate dormant GPRS sessions after a few minutes of zero traffic. Configure an empty send frame keepalive in the TIA Portal connection settings to prevent the radio from parking.
• If the S7-1200 CPU is replaced, the CP keeps its old IMSI binding in TCSB; you must delete and re-add the partner in TCSB Config or import the new TC_DB.
• Always verify the SIM card in a regular smartphone first to confirm APN, username, password, and that data is provisioned on the subscription.
• The CP 1242-7 V2 is not hot-swappable on the S7-1200. Power down before inserting/removing.
• Behind a private APN with a corporate firewall, the TCSB host may be on a different subnet; do not rely on link-local discovery — hard-code the TCSB partner IP in the TIA Portal configuration.

FAQ