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 (per CM up to 31 standard analog slaves, each with up to four channels, or up to 62 A/B analog slaves, each with up to two channels).

Operating conditions

• The CM 1243‑2 communication module exchanges data with the S7‑1200 CPU with a cycle time of 10 ms.
• The AS‑i cycle time depends on the AS‑i bus capacity and is up to 5 ms in the case of 31 standard slaves; for more information, see Manual "AS‑i Master CM 1243‑2 and AS‑i DCM 1271 Data Decoupling Module for SIMATIC S7‑1200" https://support.industry.siemens.com/cs/ww/en/view/57358958.
• 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.