S7-1200 PLC CM 1243-2 Communication module 3RK7243-2AA30-0XB0

SIEMENS SIMATIC S7-1200, CM 1243-2 communication module AS-Interface master according to AS-i specification V3.0

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Order No.: 3RK7243-2AA30-0XB0 3RK72432AA300XB0 SIMATIC S7-1200, CM 1243-2 communication module AS-Interface master according to AS-i specification V3.03RK72432AA300XB0_datasheet_en


The CM 1243‑2 communication module is the AS-Interface master for the SIMATIC S7‑1200 and has the following features:

As many as 62 AS-Interface slaves can be connected

Integrated analog value transmission

Supports all AS-Interface master functions in accordance with the AS-Interface specification V3.0

Indication of the operating state on the front of the device displayed via LED

Display of operating mode, AS-Interface voltage faults, configuration faults and peripheral faults via LED behind the front panel

Compact enclosure in the design of the SIMATIC S7‑1200

Suitable for AS‑Interface with 30‑V voltage and AS‑i Power24V: In combination with the optional DCM 1271 data decoupling unit, a standard 24 V power supply unit can be used

Configuration and diagnostics via the TIA Portal


The CM 1243‑2 communication module is positioned to the left of the S7‑1200 CPU and linked to the S7‑1200 via lateral contacts.

It has:

Terminals for two AS-i cables (internally jumpered) via two screw terminals each

One terminal for connection to the functional ground

LEDs for indication of the operating state and fault statuses of the connected slaves

The screw terminals (included in scope of supply) can be removed to facilitate installation.


The CM 1243‑2 supports all specified functions of the AS‑Interface Specification V3.0.

The values of the digital AS‑i slaves can be activated via the process image of the S7‑1200. During configuration of the slaves in the TIA Portal, the values of the analog AS‑i slaves can also be accessed directly in the process image.

It is also possible to exchange all data of the AS-i master and the connected AS-i slaves with the S7‑1200 via the data record interface.

Changeover of the operating mode, automatic application of the slave configuration and the re‑addressing of a connected AS‑i slave can be implemented via the control panel of the CM 1243‑2 in the TIA Portal.

The optional DCM 1271 data decoupling unit (see “Ordering data for accessories”) has an integrated detection unit for detecting ground faults on the AS‑Interface cable. The integrated overload protection also disconnects the AS‑Interface cable if the drive current required exceeds 4 A. For more information on DCM 1271, see “Power supplies and data decoupling units” → “Data decoupling units for S7‑1200”.

Notes on security

In order to protect plants, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art industrial security concept. Siemens products and solutions only represent one component of such a concept.

For more information on Industrial Security, see www.siemens.com/industrialsecurity.


To configure CM 1243‑2, you require STEP 7 V11 + SP2 or higher.

The software enables user-friendly configuration and diagnostics of the AS-i master and any connected slaves.

Alternatively, you can also apply the AS-Interface ACTUAL configuration at the “touch of a button” via the control panel integrated in the TIA Portal/STEP 7.

When operated on a S7‑1200 CPU with firmware version V4.0 or higher, the firmware version V1.1 (or higher) is required for the CM 1243‑2.


More flexibility and versatility in the use of SIMATIC S7‑1200 as the result of a significant increase in the number of digital and analog inputs/outputs available

Very easy configuration and diagnostics of the AS-Interface via the TIA Portal (STEP 7 V11 + SP2 or higher)

Easy operation with AS‑Interface power supply unit (see “AS‑Interface power supply units”) without restrictions

Alternatively: No need for the AS‑i power supply unit with AS‑i Power24V. The AS‑Interface cable is powered through an existing 24 V DC PELV power supply unit. For decoupling, the AS‑i DCM 1271 data decoupling module is required, see “Ordering data for accessories”. For more information see “Power supplies and data decoupling units” → “Data decoupling units for S7‑1200”.

LEDs for indication of fault statuses for fast diagnostics

Monitoring of AS-Interface voltage facilitates diagnostics


The CM 1243-2 is the AS-Interface master connection for the 12xx CPUs of the SIMATIC S7-1200. Through connection to AS‑Interface, the number of digital inputs and outputs available for the S7‑1200 is greatly increased (max. 496 DI / 496 DQ on the AS‑Interface per CM).

The integrated analog value processing also makes the analog values available at the AS‑Interface for the S7‑1200. Up to 31 analog slaves with a standard address (each with up to four channels) or up to 62 analog slaves with an A/B address (each with up to two channels) are possible per CM.

Operating conditions:

The CM 1243‑2 communication module exchanges data with the S7‑1200 CPU with a cycle time of 10 ms.

For calculation of the maximum switching frequency at inputs/outputs of AS‑i slaves, these cycle times and the runtime of the user program must be added up.

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