Siemens Simatic S7-1200 Profibus Communication Module 6GK7243-5DX30-0XE0

Siemens 6GK7243-5DX30-0XE0 | SIMATIC S7-1200 CM 1243-5 PROFIBUS DP Master Module — 16 Slaves / 12 Mbps / 9-Pin Sub-D

PROFIBUS for the S7-1200 — The Field Installed Base Problem

The S7-1200 CPU has integrated PROFINET. It has no native PROFIBUS. The CM 1243-5 is what fills that gap.

The reason this module exists is the installed base. Thousands of plants run PROFIBUS DP networks built during the 2000s and 2010s — drives, remote I/O, instruments, and safety systems wired across hundreds of metres of twisted-pair shielded cable.

When those plants upgrade their PLC controllers to S7-1200, the field devices and cabling stay. The CM 1243-5 lets the S7-1200 take over as the DP master from the legacy CPU, preserving the entire field device infrastructure. The same module is the answer when new S7-1200 installations need to connect to established Siemens drives — MICROMASTER 440, older G120 variants — that are available only with PROFIBUS interfaces.

Key Specifications

Three Communication Services on One Connector

The CM 1243-5 provides three services over its single 9-pin Sub-D:

DP cyclic I/O exchange — continuous, time-deterministic data exchange with slave devices. Typical cycle times are a few milliseconds at standard PROFIBUS speeds.

PG/OP communication — a TIA Portal programming terminal connected to the PROFIBUS bus can access the S7-1200 CPU for monitoring and programme download, without needing a separate Ethernet connection to the controller.

S7 communication (PUT/GET) — a supervisory S7-400 or other S7 PLC on the same PROFIBUS network can exchange data with the S7-1200 using native S7 protocol, without a separate Ethernet link.

CM 1243-5 vs CM 1242-5

The CM 1243-5 is a DP Master — it manages slaves. The CM 1242-5 (6GK7242-5DX30-0XE0) is a DP Slave — it makes the S7-1200 appear as a slave to a higher-level master. These are distinct modules for distinct roles.

FAQ

Q1: Can the CM 1243-5 act as a PROFIBUS DP slave as well as a master?

No. The CM 1243-5 is master-only. For the S7-1200 to act as a PROFIBUS DP slave (connecting to an upstream S7-400 or DCS as master), the CM 1242-5 (6GK7242-5DX30-0XE0) is required. These are separate modules for separate roles — the CM 1243-5 cannot be configured as a slave.

Q2: How is a PROFIBUS slave added to the CM 1243-5 configuration in TIA Portal?

Import the slave's GSD file into TIA Portal's hardware catalogue. In the network and device view, add the CM 1243-5 to the S7-1200 rack, create the PROFIBUS network, then drag the slave from the hardware catalogue onto the bus. TIA Portal reads the GSD file to determine the correct telegram structure and I/O data mapping. GSD files for Siemens products are available from the Siemens Industry Online Support (SIOS) portal; third-party GSD files come from the respective device manufacturers.

Q3: Does the CM 1243-5 need a separate 24V supply?

No. It receives 24V DC through the S7-1200 system connector on the left side of the CPU. No external power connection is required on the module itself.

Q4: Does the CM 1243-5 support isochronous PROFIBUS for motion control?

No. The CM 1243-5 supports standard DP-V1 Master Class 1 cyclic communication with typical cycle times in the millisecond range. It does not support the DP-V2 isochronous (clock-synchronous) mode required for microsecond-accurate multi-axis motion control. For isochronous motion control on PROFIBUS, dedicated motion platforms (SIMOTION, S7-300/400 with DP-V2 capable CP) are the correct solution.

Q5: Can TIA Portal diagnose PROFIBUS slave faults through the CM 1243-5?

Yes. TIA Portal's online diagnostics show the status of each configured DP slave — communicating, in error, or absent. Individual slave diagnostic data (alarm bytes, DP-V1 extended diagnostics) is accessible through the device and network online view. The CM 1243-5 also generates entries in the S7-1200's system diagnostic buffer when PROFIBUS network faults occur, providing timestamps and fault codes for root cause analysis.