The amount of transferable data per module is limited by various parameters:

  • Maximum telegram sizeA maximum of 1466 bytes of user data can be transferred per telegram and thus per connection.

  • Maximum number of pointersThe data to be transferred is defined using ANY pointers, which are transferred from ibaPDA to the controller. Here, connected operands (i.e. successive addresses) are represented by a common pointer. Depending on the size of the REQ_DB, a different number of pointers can be managed.

    • With S7-300, S7-400, WinAC controls the length can be freely selected. 5280 bytes: up to 128 pointers 9120 bytes: up to 512 pointers 14240 bytes: up to 1024 pointers (maximum)

    • Only a fixed length is provided for S7-1500 controllers: 9120 bytes: up to 512 pointers

Example

If you use a REQ_DB with a length of 9120 bytes, up to 512 pointers can be used, which may write a total address space of 1466 bytes.

If 512 distributed individual bytes of operands are to be acquired, all 512 pointers are required: Only 512 bytes can be acquired, although the maximum telegram size of 1466 bytes has not yet been reached.

If the 512 byte operands are located on successive addresses, only 1 pointer is required. There are 511 pointers available to address the remaining 1466 bytes - 512 bytes = 954 bytes.

You can find the maximum telegram size and the current maximum number of pointers in the S7 Request info tab under Diagnostics.

See also Module diagnostics.