Acyclic Memory Access - Beckhoff EP6080-0000 Documentation

Commissioning and configuration
5.4

Acyclic memory access

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. This read/write access proceeds considerably slower than the
above-described cyclic memory access.
The created structure can only be changed in the status PREOP. It can also be generally locked to prevent
further changes.
Background information: The entire memory capacity is administered in the form of CoE objects (CAN over
EtherCAT). The administration data (number and byte size) is located in the object index 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:
• Calculation of the storage space [} 26]
• Definition of the memory objects via the StartUp list [} 27]
• Access to the memory objects during operation [} 31]
Calculation of the memory space
The available 128 KB (131,072 bytes) of memory are subdivided as follows:
• 1280 bytes for the cyclic data
• 2000 bytes for internal administration
• x bytes as defined by the user for the acyclic data in the following
• y bytes: a shadow buffer as large as the largest memory object is kept on standby in the background.
Sample: The acyclic memory objects Obj1, Obj2 and Obj3 are defined with 1,000, 3,000 and 7,000 bytes
respectively --> x = 11,000 bytes and y = 7,000 bytes. Thus 113,072 bytes of memory space remain.
26 Version: 1.0 EP6080-0000