Does the specification "340 Byte Input or Output Data" relate to the total data that the user can send?
In early versions of the PROFINET stack the available net data amount is 320 bytes. The specification of 340 bytes is related to total data, including header information. Since stack V1.4, the maximum amount of net data is 1016 bytes for a total of two application relations (AR). For example, one AR may have 1014 bytes, while the other AR has only 2 bytes.