In EtherCAT it is possible to configure object entries larger than 30 bytes. For example, subindexes configured as arrays with more than 30 elements defined using the OCTET STRING datatype. In this case, the first 30 bytes shall be mapped to the configured subindex and the remaining bytes shall be mapped to the next subindex. This feature is demonstrated by creating an array object with 51 bytes and mapping to RXPDO.
Create a variable object at index 0x3001 as an array with 51 elements defined with OCTETSTRING data type.
Map the above created object to RxPDO created at index 0x1602.
The below diagram shows the RxPDO object in the CoE online tab in TwinCAT. The first 30 bytes (240 bits) are mapped to subindex 01 and the remaining 21 bytes (168 bits) are mapped to subindex 02. Note that index is 0x0000 in the value column of the subindex 02 as a result of large object padding.
The below diagram shows the RxPDO object in the process data tab in TwinCAT. Observe the Index,size and offset values in PDO content.