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Beginning with version 2.1 of the module firmware it is possible for all protocol stacks to extend the possible process data size using RPC transport. This feature allows significantly increasing the size of process data beyond the boundaries of the cyclic channel (73 bytesByte). However, process data using the RPC transport come with a significant cut in performance.
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The cyclic channel provides up to 73 bytesByte, however in the direction of output data additionally a 4 byte generic data provider is mapped, which contains status information (LEDs, connection status, Update counter). |
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Using RPC transport limits the update cycle of process data, which is mapped to RPC, to a smaller value. Typically, an update cycle of around 100ms 100 ms is possible (see figure below). For objects, mapped to the data mapper, the update cycle (depending on the application controller (AC)) is 1 ms.
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For EtherCAT the theoretical maximum data size is 1408 BytesByte, but it’s limited by the available memory.
For EtherNet/IP the maximum data size is 512 bytes505 Byte O->T and 509 Byte T-->O.
The update cycle for process data mapped to RPC depends on the amount of data required to update. Following table shows typical values where the amount of data is mapped to both communication directions (input data and output data) and all data is required to be updated in one cycle. The time required can reach 310ms310 ms, see table below.
used module size per direction | average cycle time |
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Octet string 1434 Byte | 310 ms |
Octet string 1024 Byte | 230 ms |
Octet string 512 Byte | 125 ms |
Octet string 256 Byte | 70 ms |
Octet string 128 Byte | 40 ms |
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