Siemens SIMATIC S7 Manual page 37

DATA_TYPE
START_ADDRESS
LENGTH
MODBUS / TCP communication via the integrated PN interface of the CPU
2XV9450-1MB02; Manual edition 2.1
The parameter DATA_TYPE defines which Modbus data type is to be
accessed with the current job. The following data types are available:
Coils
Inputs
Holding Register
Input Register
In the operating mode S7 is Client, DATA_TYPE is an input parameter. In the
operating mode S7 is Server, DATA_TYPE is an output parameter.
The different data types are related directly to the used function codes.
Data type DATA_
TYPE
Coils
Coils
Coils
Coils
Inputs
Holding Register
Holding Register
Holding Register
Holding Register
Input Register
The parameter START_ADDRESS specifies the first MODBUS address that
is read or written.
In the operating mode S7 is Client, this is an input parameter. In the
operating mode S7 is Server, this is an output parameter.
The parameter LENGTH specifies the number of MODBUS values that are
read or written.
In the operating mode S7 is Client, this is an input parameter. In the
operating mode S7 is Server, this is an output parameter.
With a reading function, a maximum of 125 registers or 2000 bits is possible
per telegram. With a writing function, a maximum of 100 registers or 800 bits
is possible.
For each telegram, all registers or bits have to be in the same DB.
B#16#1
B#16#2
B#16#3
B#16#4
Function Length
1 read any
1 write
1 write
1 write
2 read any
3 read any
3 write
3 write
3 write
4 read any
Function Block MODBUSPN
single_ Function
write code
irrelevant
1 TRUE
1 FALSE
>1 irrelevant
irrelevant
irrelevant
1 TRUE
1 FALSE
>1 irrelevant
irrelevant
1
5
15
15
2
3
6
16
16
4
6-11