Data traffic with acyclic CoE access

In acyclic access, the user can create up to 255 memory objects that may also be differently sized. These objects can be specifically accessed from the PLC task via acyclic SDO access (Service Data Objects) for writing or reading; see sample program in chapter Online access to the memory objects during operation. This read/write access proceeds considerably slower than the above-described cyclic memory access.

The created structure can only be changed in the module status PREOP. It can also be generally locked to prevent further changes.

Background information:
All storage space is managed in the form of CoE objects (CAN over EtherCAT). The administration data (number and byte size) is located in the Object 0x2F00 with its subindexes; the stored data itself in the CoE objects from 0x2000: 0x2000, 0x2008, 0x2010, 0x2018 etc.

A memory object in acyclic access can comprise 1 to 8190 bytes.

The following procedure is recommended in order to use acyclic access:

1. Calculation of the storage space
2. Definition of the memory objects via the StartUp list
3. Access to the memory objects during operation