Entry type: FAQ, Entry ID: 58378237, Entry date: 11/26/2014
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Which blocks for Modbus TCP can you rename or re-wire when the block numbers of the Modbus blocks are already being used in the user program?

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Description
The blocks that are available for Modbus communication with SIMATIC S7 are delivered with a unique block number.
If there are already blocks in the user program that have these block numbers, there is a block number conflict.

Please proceed as follows to avoid this conflict.

  • You can rename the Modbus blocks that are called directly in the user program.
  • You cannot rename the blocks that are called internally in the Modbus blocks. You have to re-wire those blocks.

The table below shows the Modbus blocks that you can rename or re-wire.
 

Product Article no. Modbus block > rename Block called internally from the Modbus library > re-wire Block called internally from the Standard / SIMATIC NET library > re-wire
Modbus/TCP CP 2XV9450-1MB00 FB108 FB106, FB107 AG_(L)SEND
AG_(L)RECV
EQ_STRNG(*)
AG_CNTRL(**)
Modbus/TCP RED V2 2XV9450-1MB11 FB909, FB907 FB908, FB906 AG_(L)SEND
AG_(L)RECV
EQ_STRNG(*)
AG_CNTRL(**)
Modbus/TCP PN CPU 2XV9450-1MB02 FB102 FB103, FB104, FB105 TSEND
TRCV
TCON
TDISCON
EQ_STRNG(*)
Modbus/TCP PN CPU Redundant 6AV6676-6MB10-0AX0 FB915, FB917 FB913, FB914, FB916 TSEND
TRCV
TCON
TDISCON
Modbus/TCP SENTRON PAC 6AV6676-6MA30-0AX0
6AV6676-6MA30-1AX0
6AV6676-6MA30-2AX0
FB109, FB110, FB111 FB99, FB103, FC99 TSEND
TRCV
TCON
TDISCON
TUSEND
Table 01

(*) The EQ_STRNG block is only in older versions of the product.
(**) If both EQ_STRNG and AG_CNTRL are used by the Modbus blocks are used, then AG_CNTRL is already re-wired in the Modbus library. More information about this is available in the relevant product manual.

You must follow a specific order when re-wiring the blocks that are called internally in the Modbus blocks. Re-wire the blocks - if necessary - in the order listed.

  1. EQ_STRNG, AG_CNTRL, AG_(L)SEND, AG_(L)RECV, TSEND, TRCV, TCON, TDISCON
  2. Internally called blocks (FB106, FB107, FB1734, FB908, FB906, FB103, FB104, FB105, FB913, FB914, FB915, FB99, FB103, FC99)
  3. Remaining blocks

You do not have to re-wire all the blocks. Even if you re-wire only a few internally called blocks, you must nevertheless keep to the order given above. In this case, you leave out the blocks that are not re-wired.