S7-1200 PROFIBUS Master-Slave Data Exchange in TIA Portal V13

Overview

Engineers frequently attempt to establish an S7 connection between two SIMATIC S7-1200 CPUs over PROFIBUS using the PUT and GET instructions in TIA Portal V13. The portal blocks the configuration, and the resulting error is not a configuration mistake: S7 communication is not supported on the PROFIBUS interface of an S7-1200. The Siemens TIA Portal documentation for configuring PROFIBUS DP with S7-1200 states that the PROFIBUS CM on an S7-1200 acts strictly as a DP master (CM 1243-5) or DP slave (CM 1242-5) for distributed I/O, and the S7 connection resources exposed by the CPU are bound to the PROFINET interface, not the PROFIBUS CM.

The correct method to exchange data between two S7-1200 stations over PROFIBUS is the I-Slave/Master model with configured transfer areas, polled by the master CPU using the DPRD_DAT (read) and DPWR_DAT (write) instructions. This article walks through hardware selection, project configuration in TIA Portal V13, transfer-area setup, and the program code required to read a value (for example, the constant 100) from a slave CPU to a master CPU.

Why S7 PUT/GET Fails Over PROFIBUS on the S7-1200

The S7-1200 connection resources are managed by the CPU firmware. With the default firmware delivered for a 1214C, the CPU exposes a fixed number of communication connections (typically 16 for the 1214C/1215C/1217C variants), but those connections are PROFINET-only. When you add a CM 1242-5 (slave) or CM 1243-5 (master) to the S7-1200, the module does not extend the S7 connection table; it only adds a DP master or DP slave interface for cyclic I/O data exchange.

Symptoms engineers see in TIA Portal V13:

• The "Add new connection" dialog only allows PROFINET partners when the local interface is a PROFIBUS CM.
• PUT and GET blocks either refuse to compile, or compile but never transition from BUSY to DONE at runtime because no S7 connection is bound.
• Online diagnostics on the CM show the DP bus is operational, but no S7 connection is listed in "Connection resources".

Prerequisites

Confirm the following before configuring the project:

Hardware and Module Pinout Reference

The CM 1242-5 (slave) and CM 1243-5 (master) plug into the left-side bay of the S7-1200 CPU. The PROFIBUS connector is a 9-pin D-sub female. Pin assignment is identical to the standard PROFIBUS DP connector:

Project Setup in TIA Portal V13

1. Create a new project and add both S7-1200 CPUs. Name them clearly, e.g., CPU_Master and CPU_Slave.
2. In the device configuration of the master, drag a CM 1243-5 from the hardware catalog onto the left of the CPU. TIA Portal auto-assigns a PROFIBUS interface with subnet PROFIBUS_1.
3. In the device configuration of the slave, drag a CM 1242-5. Connect its PROFIBUS interface to PROFIBUS_1.
4. Open the master CM's properties → PROFIBUS address: set to 1, transmission rate 1.5 Mbps (or whatever the segment requires).
5. Open the slave CM's properties → PROFIBUS address: set to 2.
6. From the device view of the slave CM, switch the operating mode to DP slave. In the I-Slave communication tab, the transfer areas are configured in the next step.

Configuring the DP Slave (I-Slave Mode) and Transfer Areas

The I-Slave mode is what enables peer-to-peer data exchange between two S7-1200 stations. The slave publishes one or more transfer areas to the bus, and the master reads/writes those areas as if they were remote I/O.

1. Select the CM 1242-5 in the slave station.
2. Open Properties → I-Slave communication.
3. Add a new transfer area:
   • Type: Input (data the slave provides to the master)
   • Length: e.g., 4 bytes
   • Address in slave process image: e.g., %IW100
4. Optionally add an output transfer area for data the master sends back to the slave (length 4 bytes, e.g., %QW100).
5. Compile and download the slave configuration.

Configuring the DP Master and Assigning the Slave

1. Switch to network view and connect the master CM 1243-5 to the slave CM 1242-5 on the same PROFIBUS subnet.
2. Right-click the master CM → Assign master system, then drag the slave CM into the master system.
3. Open the slave device in the device view of the master project. TIA Portal lists the transfer areas as slot 0 with input/output subslots, matching the I-Slave configuration on the slave.
4. The slave's transfer areas appear in the master's device view at I addresses (e.g., IW0) and Q addresses (e.g., QW0). These are the addresses the master program uses with DPRD_DAT/DPWR_DAT.

Programming: Reading a Value from the Slave with DPRD_DAT

The DPRD_DAT instruction reads a consistent block of data from a DP slave. The DPWR_DAT instruction writes a consistent block of data. Both are available in the Instructions task card under Communication → PROFIBUS DP.

Example: read 4 bytes from slave PROFIBUS address 2, slot 0, and place the result in a tag called SlaveData.

// Master CPU - program block OB1 (ladder / FBD / ST)
// Read 4 bytes from DP slave at PROFIBUS address 2, slot 0
// RECORD = target tag; LADDR = configured I address of the slave

// Ladder equivalent:
// [ DPRD_DAT_EN ]----[ ENO ]
//     LADDR  := 0          // I/O start address from device view
//     RECORD := P#DB1.DBX0.0 BYTE 4   // 4-byte destination
//     RET_VAL:= MW100       // return value (16-bit status)

// Structured Text:
IF "FirstScan" THEN
    "DPRD_DB".REQ := TRUE;
END_IF;

"DPRD_DB"(REQ := "FirstScan",
         LADDR := 0,
         RECORD := P#"SlaveData".InputWord BYTE 4,
         RET_VAL := "DPRD_Status");

IF "DPRD_DB".DONE THEN
    "ValueFromSlave" := "SlaveData".InputWord;
    "DPRD_DB".REQ := FALSE;
END_IF;

IF "DPRD_DB".ERROR THEN
    "ProfibusError" := "DPRD_DB".STATUS;
END_IF;

To send a value (e.g., 100) from the master to the slave, mirror the configuration with a write transfer area on the slave and use DPWR_DAT on the master:

// Structured Text - master program
"ValueToSlave" := 100;

"DPWR_DB"(REQ := TRUE,
         LADDR := 4,                       // Q start address of output transfer area
         RECORD := P#"MasterData".OutputWord BYTE 4,
         RET_VAL := "DPWR_Status");

IF "DPWR_DB".DONE THEN
    "DPWR_DB".REQ := FALSE;
END_IF;

On the slave CPU, map the input transfer area into a tag (e.g., %IW100) and copy it into a data block. The slave can also react to changes in %IW100 to drive outputs, store values, etc.

Reading Data on the Slave CPU

The slave CPU sees its own transfer area as a normal input area in the process image. To expose the data received from the master (the value 100 in the example) as a tag, simply read %IW100 in the slave program. To make the tag available for the master, store it in the input transfer area region (e.g., %QW100 of the slave, which is mapped to the master as an input).

// Slave CPU - OB1 (Structured Text)
// Push a constant 100 into the transfer area so the master can read it.
"ValueToMaster" := 100;
// Tag "ValueToMaster" must be at the address configured as the input transfer area,
// e.g., %QW100 (4 bytes), in the CM 1242-5 I-Slave configuration.

On the master, the previously written DPRD_DAT will read this 4-byte region and the value 100 will appear in SlaveData.InputWord.

Diagnostic and Status Codes

The STATUS output of DPRD_DAT/DPWR_DAT returns a 16-bit value. The most common codes you will see on S7-1200:

PROFIBUS module LEDs provide additional clues:

• BF (red, steady): bus fault — cable/termination/addressing issue.
• BF (red, flashing): slave configuration mismatch.
• SF (red): system fault on the CM; check online diagnostics.
• ON (green): the CM is in data exchange with the master.

Troubleshooting Matrix

Alternative: Switch to PROFINET for S7 Communication

If the project permits, replacing the PROFIBUS CMs with a direct PROFINET connection between the two S7-1200 CPUs unlocks the standard PUT/GET/TSEND/TRCV instruction set. In that scenario:

• The S7-1200 PROFINET interface is used for S7 communication.
• No CM is required.
• PUT and GET are configured via the "Connections" editor against the partner CPU's PROFINET IP address.

For installations with existing PROFIBUS infrastructure (cable, connectors, SCADA interfaces) staying on PROFIBUS and using the I-Slave / DPRD_DAT/DPWR_DAT method is usually the lowest-impact change.

Verification

1. Compile and download both stations. The master CPU must be in RUN.
2. Open "Online & Diagnostics" on the master CM 1243-5. The "DP master system" view should list the slave at PROFIBUS address 2 with state Data exchange.
3. Force REQ on the DPRD_DAT instance. Watch STATUS transition from 7001 → 0000 with DONE = TRUE.
4. Watch table on the master: SlaveData.InputWord should display the value 100 within one DP cycle.
5. On the slave, watch table: writing to the output transfer area tag (e.g., QW100) should be reflected on the master at the corresponding input address within one cycle.
6. Disconnect the PROFIBUS cable at one end: the master should report STATUS = 80A1 and the CM's BF LED should light. Reconnect: communication resumes within the configured reaction time.