Siemens SIMATIC S7-1200 System Manual page 1202

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Communication processor and Modbus TCP

13.5 Modbus communication

For "Extended Addressing" mode the maximum data lengths are reduced by 1 byte or 1 word depending upon the data

type used by the function.

DATA_PTR parameter

The DATA_PTR parameter points to the DB or M address that is written to or read from. If

you use a data block, then you must create a global data block that provides data storage for

reads and writes to Modbus slaves.

The DATA_PTR data block type must allow direct addressing

The data block must allow both direct (absolute) and symbolic addressing. When you create

the data block the "Standard" access attribute must be selected.

Data block structures for the DATA_PTR parameter

● These data types are valid for word reads of Modbus addresses 30001 to 39999, 40001

to 49999, and 400001 to 465536 and also for word writes to Modbus addresses 40001 to

49999 and 400001 to 465536.

– Standard array of WORD, UINT, or INT data types

– Named WORD, UINT, or INT structure where each element has a unique name and

– Named complex structure where each element has a unique name and a 16 or 32 bit

● For bit reads and writes of Modbus addresses 00001 to 09999 and bit reads of 10001 to

– Standard array of Boolean data types.

– Named Boolean structure of uniquely named Boolean variables.

● Although not required, it is recommended that each Modbus_Master instruction have its

own separate memory area. The reason for this recommendation is that there is a greater

possibility of data corruption if multiple Modbus_Master instructions are reading and

writing to the same memory area.

● There is no requirement that the DATA_PTR data areas be in the same global data block.

You can create one data block with multiple areas for Modbus reads, one data block for

Modbus writes, or one data block for each slave station.

Operation and data

Reset slave event counter using data diagnostic code

1 word per request

16 bit data type.

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK