Siemens S7-1200 System Manual page 753

MODE Modbus Data length
Function
81 08 1
3 to 10,
12 to 79,
82 to 255
For "Extended Addressing" mode the maximum data lengths are reduced by 1 byte or 1 word depending upon the data
1
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.
Note
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
● For bit reads and writes of Modbus addresses 00001 to 09999 and bit reads of 10001 to
● Although not required, it is recommended that each MB_MASTER instruction have its
● There is no requirement that the DATA_PTR data areas be in the same global data block.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
Operation and data
Reset slave event counter using data diagnostic code
0x000A
1 word per request
Reserved
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
16 bit data type.
– Named complex structure where each element has a unique name and a 16 or 32 bit
data type.
19999.
– Standard array of Boolean data types.
– Named Boolean structure of uniquely named Boolean variables.
own separate memory area. The reason for this recommendation is that there is a greater
possibility of data corruption if multiple MB_MASTER instructions are reading and writing
to the same memory area.
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.
Communication processor and Modbus TCP
12.5 Modbus communication
Modbus
Address
753